# The Colour of Light

Curious6
I have been pondering about the nature of colour and its philosophical status as either an irreducible, objective property of an object or rather as a derived quality, dependent on the perceiver. Basically, to put it in Lockeian terms, the question is whether colour is a 'primary' or a 'secondary' qualit. I know Locke and others considered it a secondary quality, but I have been thinking about a scenario where colour does indeed seem an intrinsic property.

Normally people say colour is the result of different wavelengths of light being absorbed and reflected by the constituents of a body, giving it a particular colour. However, consider the following scenario. You are in a dark room, no light enters and therefore it is pitch black. Then, a light from a source at the back of the room is emitted. You perceive the light, and it has its usual colour (i.e. white or yellowish-white). The light reaches you straight from the source, so the colour you see is not the result of wavelengths of light being absorbed by a material and the rest being reflected back. It actually does seem the light is objectively coloured in this case.

Does anybody seem any flaw or any important details I overlooked in this simple thought experiment which would invalidate the view that light is an intrinsic property of the world rather than secondary and derived?

Smurf
There's no such thing as 'light' as a distinct, separate entity. Light is just a specific range of frequencies of waves. Whichever range of waves the source of the light is emitting is the range that you will see.

'White' light is the color of all colors together (black is the complete absence of light - and therefor color). When light bounces off of a surface the surface absorbs some colors, and reflects other ones, which is what you see. So if nothing is absorbed you will see the color of the original wavelength emitted... in the case of your example.. white/yellowish.

I don't know if this belongs in the philosophy section.

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Curious6
The question posed before is a philosophical question par excellence, and it is therefore appropriate under this section. Anyways, light is a stream of photons exhibiting a wave-particle duality, as noted by quantum physics. Your answer referred to seeing the colour of objects, but what I was referring to was the actual colour of light, as light itself does not have to be reflected off other bodies in order to be perceived. Is light (this stream of photons) already coloured in your view? Comments and other input by others regarding this question could be useful.

Gold Member
The light travels as whatever wavelength it has, it does not need a medium for it to exist. If a red light wave is coming towards you, it does not need to reflect off anything to be perceived as red light in your eyes. Think of the photoelectric effect!

Smurf
Curious6 said:
Yes, as Pengwuino said, Light is colored, and does not require a medium to be perceived as a color.

gerben
The colors that we see depend on the wavelength of the light that enters our eyes. The color of an object depends on its reflectance properties. I think it is not right to say that light is colored. You should say light has a certain wavelength (a certain band of wavelengths), and the colors that we perceive depend on those wavelengths.

Consider an animal other than a human with differently built eyes. It will see different colors when you shine the lamp in its eyes.

Smurf
gerben said:
The colors that we see depend on the wavelength of the light that enters our eyes. The color of an object depends on its reflectance properties. I think it is not right to say that light is colored. You should say light has a certain wavelength (a certain band of wavelengths), and the colors that we perceive depend on those wavelengths.

Consider an animal other than a human with differently built eyes. It will see different colors when you shine the lamp in its eyes.
Whatever... the point is they're already wavelengths and don't need to bounce off of something.

And I don't really see the point in your post, why can't we say it is colored. Color is the name we give to the reflectable attributes. And they're universal, someone/thing with different built eyes might see the light differently but they still recognize the different wavelengths the same way we do, so it doens't matter.

Burnsys
Every time an electron jump to a lower orbit a photon is emited, depending from what orbit did the electron jumped, diferent the wavelenght of the photon and so it's color. You can check on neon lights, depending on the gas the electron are flowing to, diferent the color of the light, becouse of the electron distribution of it's atoms......

zoobyshoe
Curious6 said:
Does anybody seem any flaw or any important details I overlooked in this simple thought experiment which would invalidate the view that light is an intrinsic property of the world rather than secondary and derived?
The color of light is created in our brains. There is nothing inherent in the different frequencies that should make blue so different than red, and red than yellow. The differences in frequencies are simply faster or slower: all we can account for by the difference in frequency is shades of grey.

The eyes and brain select different ranges of wavelengths and turn them into the spectacular, and pretty much fictional, qualitative experience we know as color.

"In 1957, ninety-odd years after Maxwell's famous demonstration, Edwin Land - not merely the inventor of the instant Land camera and Polaroid, but an experimenter and theorizer of genius - provided a photographic demonstration of color perception even more startling. Unlike Maxwell, he made only two black-and-white images (using a split-beam camera so they could be taken at the same time from the same viewpoint, through the same lens) and superimposed these on a screen with a double lens projector. He used two filters to make the images: one passing longer wavelengths (a red filter), the other passing shorter wavelengths (a green filter). The first image was then projected through a red filter, the second with ordinary white light, unfiltered. One might expect that this would produce just an over all pale-pink image, but something impossible' happened instead. The photograph of a young woman appeared instantly in full color - blonde hair, pale blue eyes, red coat, bluegreen collar, and strikingly natural flesh tones,' as Land later described it. Where did these colors come from, and how were they made? They did not seem to be in' the photographs or in the iluminants themselves. These demonstrations, overwhelming in their simplicity and impact were color illusions' in Goethe's sense, but illusions that demonstrated a neurological truth - that colors are not out there' in the world, nor (as classical thery held) an automatic correlate of wavelength, but, rather, are constructed by the brain."

Oliver Sacks

An Anthropologist On Mars
p.24 Vintage Books, 1995

Smurf
Ah Zooby, I knew there was a reason I liked you!

gerben
Smurf said:
Whatever... the point is they're already wavelengths and don't need to bounce off of something.

And I don't really see the point in your post, why can't we say it is colored. Color is the name we give to the reflectable attributes. And they're universal, someone/thing with different built eyes might see the light differently but they still recognize the different wavelengths the same way we do, so it doens't matter.
The point is that only the observer makes them colors. The observer interprets the combination of wavelengths as colors. Light in itself is not colored. Color is an interpretation, based on the wavelengths in the light originating from the object you assigned the color to and also on the wavelengths originating from its surroundings.

Land's experiments corroborate that.

gerben
The color of a certain part of a scene is probably a function of the spectral content of the whole scene.

Finding this function is the (currently not yet achieved) aim of color vision research.

El Hombre Invisible
Just to throw my ha'penny in (stingy bast that I am), not only is 'colour' merely an interpretation of the frequency of the EM wave but also, to contradict Smurf's statement "[w]hichever range of waves the source of the light is emitting is the range that you will see", two different observers may disagree as to the colour of that light. In cosmological redshift, for instance, the frequency of light emitted (i.e. in a reference frame in which the source is at rest) is greater than that in which it is received by receding observers in distant galaxies (i.e. in a reference frame in which the observer is at rest). Therefore 'colour' cannot be said to be an intrinsic quality of light, since even frequency and wavelength are relative properties.

Royce
Curious6 said:
I have been pondering about the nature of colour and its philosophical status as either an irreducible, objective property of an object or rather as a derived quality, dependent on the perceiver. Basically, to put it in Lockeian terms, the question is whether colour is a 'primary' or a 'secondary' qualit. I know Locke and others considered it a secondary quality, but I have been thinking about a scenario where colour does indeed seem an intrinsic property.

Curious6, I have long thought that color is intrinsic. There are a number of reasons that I think this way.

First, photons are messenger particles or wave particles if you prefer. They have no intrinsic wavelength or color of their own but carry the wave length as a function of the energy state of the electron that emitted them. Some are also absorbed by the medium through which they pass carrying that information with them also. If we measure that light we can learn a great deal about the emitter as well as the intervening gases or medium. I'm sure that you are aware of all of this, but the point is that photons carry information and do not have any specific wavelenght or color themselves.

Second, we did not and do not invent color nor change the color that we see.
Its true that our minds try to compensate for background color and contrasts so that our color perception changes from what is actually received, seen,but humans are not the only animals that see color and the color that we do see for the most part is perceived the same or nearly the same for everyone. If this were not the case paintings photographs and TV would not look the same for everyone and wouldn't make any sense. For us to see and perceive the same color it must be a property of that which we are seeing and not merely some mental perception of our minds.

Third, we are evolved animals and as I said we did not invent color but evolved to detect and see that which is already there and a property of the world around us. We developed color perception because color is there and is useful information. It is an intrinsic part of our environment.

Forth, take our favorite example of color, the rose; roses breed true to their color and by interbreeding or controlling pollination we can make hybrids of different colors but we cannot breed a blue rose because roses do not have a "blue" gene. This proves that there is some property of roses that is intrinsic and genetic and we call that property color. If color were just perceived then why or how could roses or any other flower, bird, fish etc develop a gene that determines their color and passes it on to their off spring. It must therefore be intrinsic.

Curious6
Smurf said:
Yes, as Pengwuino said, Light is colored, and does not require a medium to be perceived as a color.

Yes, but how can you be sure that light itself is actually coloured, and not that the stream of photons composing it is actually colourless and that it just acquires its colour, as we observe it, through the interplay between the properties of the photons (i.e. wavelength and frequency) and the receptor (the eye/brain system)? Basically, what I am trying to say is that the properties of the photon can trigger a system when perceived by the eye that creates the colour 'yellow' or 'white', for instance, in our brain.

Curious6
zoobyshoe said:
The color of light is created in our brains. There is nothing inherent in the different frequencies that should make blue so different than red, and red than yellow. The differences in frequencies are simply faster or slower: all we can account for by the difference in frequency is shades of grey.

The eyes and brain select different ranges of wavelengths and turn them into the spectacular, and pretty much fictional, qualitative experience we know as color.

"In 1957, ninety-odd years after Maxwell's famous demonstration, Edwin Land - not merely the inventor of the instant Land camera and Polaroid, but an experimenter and theorizer of genius - provided a photographic demonstration of color perception even more startling. Unlike Maxwell, he made only two black-and-white images (using a split-beam camera so they could be taken at the same time from the same viewpoint, through the same lens) and superimposed these on a screen with a double lens projector. He used two filters to make the images: one passing longer wavelengths (a red filter), the other passing shorter wavelengths (a green filter). The first image was then projected through a red filter, the second with ordinary white light, unfiltered. One might expect that this would produce just an over all pale-pink image, but something impossible' happened instead. The photograph of a young woman appeared instantly in full color - blonde hair, pale blue eyes, red coat, bluegreen collar, and strikingly natural flesh tones,' as Land later described it. Where did these colors come from, and how were they made? They did not seem to be in' the photographs or in the iluminants themselves. These demonstrations, overwhelming in their simplicity and impact were color illusions' in Goethe's sense, but illusions that demonstrated a neurological truth - that colors are not out there' in the world, nor (as classical thery held) an automatic correlate of wavelength, but, rather, are constructed by the brain."

Oliver Sacks

An Anthropologist On Mars
p.24 Vintage Books, 1995

Very interesting indeed. However, if that experiment was supposed to definitely prove colours are an illusion created by the brain and not an 'automatic correlate of wavelength', why is there still a controvery or debate among the philosophical community about the objective nature of colour?

Also, could you please explain in slightly more detail what exactly this experiment proved. Is it saying that wavelengths trigger a mechanism in our brain which account for us seeing a particular colour for each particular wavelength?

Curious6
Royce said:
Curious6, I have long thought that color is intrinsic. There are a number of reasons that I think this way.

First, photons are messenger particles or wave particles if you prefer. They have no intrinsic wavelength or color of their own but carry the wave length as a function of the energy state of the electron that emitted them. Some are also absorbed by the medium through which they pass carrying that information with them also. If we measure that light we can learn a great deal about the emitter as well as the intervening gases or medium. I'm sure that you are aware of all of this, but the point is that photons carry information and do not have any specific wavelenght or color themselves.

Agreed.

Royce said:
Second, we did not and do not invent color nor change the color that we see.
Its true that our minds try to compensate for background color and contrasts so that our color perception changes from what is actually received, seen,but humans are not the only animals that see color and the color that we do see for the most part is perceived the same or nearly the same for everyone. If this were not the case paintings photographs and TV would not look the same for everyone and wouldn't make any sense. For us to see and perceive the same color it must be a property of that which we are seeing and not merely some mental perception of our minds..

Could be the result of evolutionary factors. Sight and the ability to assign a particular colour to different wavelenghts undoubtedly provided a competitive edge, thereby allowing this trait to be passed on to subsequent generations, until it became widespread and common to all humans.

Royce said:
Third, we are evolved animals and as I said we did not invent color but evolved to detect and see that which is already there and a property of the world around us. We developed color perception because color is there and is useful information. It is an intrinsic part of our environment.

But is it really an intrinsic property of the world? Again, as other posters in this thread have noted, is a colour not just an invention by the brain used to differentiate between varying wavelenghts?

Royce said:
Forth, take our favorite example of color, the rose; roses breed true to their color and by interbreeding or controlling pollination we can make hybrids of different colors but we cannot breed a blue rose because roses do not have a "blue" gene. This proves that there is some property of roses that is intrinsic and genetic and we call that property color. If color were just perceived then why or how could roses or any other flower, bird, fish etc develop a gene that determines their color and passes it on to their off spring. It must therefore be intrinsic.

Again, not necessary. Roses could just have developed in a way that its petals are constituted of particles that would absorb and reflect the necessary wavelenghts to produce the impression of the colour rose in our minds. The reason then which would explain why roses would not have a distinct 'blue' gene is that the constituents of the petals would all have to change in order for the wavelengths of light to be absorbed and reflected back to create the colour blue.

Staff Emeritus
Gold Member
Perceived, qualitative color is a function of the activity of the visual processing stream in the brain. Any number of visual illusions will show this to be the case. Light waves themselves do not have some sort of qualitative color; they merely have various wavelengths. The brain constructs color perceptions from various combinations of light wavelengths that strike the retina, but it is not true that there is always a simple, straightforward mapping from light wavelength of the visual scene to perceived color.

One can find a good demonstration of this here. This site features three different color illusions, wherein we can plainly see that color perception of objects is fluid and depends largely on the context of the given scene. Note that the objective properties of your computer monitor, including the wavelengths of light striking your retinas, are held constant in these demonstrations. What is changing is the context in which certain features of the scene are viewed, and this changes the manner in which we perceive the colors of these features. For each masked and unmasked scene, is one color perception 'right' and the other 'wrong'? If so, which is 'right,' and why? I think the answer is clearly that there is no 'right' way to perceive these colors. Both ways of perceiving the relevant colors are just interpretations of the visual scene created by the brain. If this were not the case, we should not expect our color perceptions to change so fluidly and radically by simply changing some of the surrounding visual context.

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Burnsys
hypnagogue said:
Perceived, qualitative color is a function of the activity of the visual processing stream in the brain. Any number of visual illusions will show this to be the case. Light waves themselves do not have some sort of qualitative color; they merely have various wavelengths. The brain constructs color perceptions from various combinations of light wavelengths that strike the retina, but it is not true that there is always a simple, straightforward mapping from light wavelength of the visual scene to perceived color.

One can find a good demonstration of this here. This site features three different color illusions, wherein we can plainly see that color perception of objects is fluid and depends largely on the context of the given scene. Note that the objective properties of your computer monitor, including the wavelengths of light striking your retinas, are held constant in these demonstrations. What is changing is the context in which certain features of the scene are viewed, and this changes the manner in which we perceive the colors of these features. For each masked and unmasked scene, is one color perception 'right' and the other 'wrong'? If so, which is 'right,' and why? I think the answer is clearly that there is no 'right' way to perceive these colors. Both ways of perceiving the relevant colors are just interpretations of the visual scene created by the brain. If this were not the case, we should not expect our color perceptions to change so fluidly and radically by simply changing some of the surrounding visual context.

Damn, i won't belive in my eyes anymore!!! or should i say my brain....

zoobyshoe
Curious6 said:
However, if that experiment was supposed to definitely prove colours are an illusion created by the brain and not an 'automatic correlate of wavelength', why is there still a controvery or debate among the philosophical community about the objective nature of colour?
You'll have to address that question to the philosophical community.
Also, could you please explain in slightly more detail what exactly this experiment proved. Is it saying that wavelengths trigger a mechanism in our brain which account for us seeing a particular colour for each particular wavelength?
All the experient proved was that color isn't an objective property of light, but an experience primarily created in the brain (via wavelength selection by the eyes). It didn't explain how.

The next generation of experiments explored how the experience of color is dependent on context, as detailed by hypnagogue in his excellent post. Any accomplished artist can verify this: the effect of a color can be grossly modified by what colors you place next to it.

The important thing to realize is that there is nothing about wavelengths of light between, say 400 and 430 nm that requires it to be percieved as blue rather than blue, or blue.

The wavelengths reflected by a particular object are objective and measurable, but what our brains make of those frequencies, how it processes them into the experience of color, is splendid fiction.

Compare to sound. Take the example of a note on a clarinet. A smooth increase in the frequency of a clarinet tone results in a smooth increase in pitch. If we we percieved sound the same way we percieve color we would encounter "thresholds" where an increase in frequency would result in the clarinet suddenly, inexplicably changing in total sound quality, so that it sounded, variously, like a violin, a trumpet, a bag pipe, a flute, and so on. There would be nothing measurable to account for these drastic shifts in qualitative experience beyond shift in frequency and wavelength. Therefore, the brain must be selecting these different ranges out and presenting them to consciousness as much more different from each other than they actually are.

The story where I got the quote about Edwin Land is about an artist who became completely colorblind after a blow to the head in a car accident. Nothing whatever happened to his eyes, only a part of his brain was damaged. It's the first chapter of that book by Sacks, An Anthropologist on Mars and is entitled The Case of the Colorblind Painter. I think most libraries carry his books.

If you're interested in color perception you might also read his book: The Island of the Colorblind, which is about a remote pacific island where a genetic predisposition to total colorblindness affects a large part of the population. The difficulties this condition causes the sufferers underscores why natural selection would favor any and all born with color vision.

Royce
Curious6 said:
Could be the result of evolutionary factors. Sight and the ability to assign a particular color to different wavelengths undoubtedly provided a competitive edge, thereby allowing this trait to be passed on to subsequent generations, until it became widespread and common to all humans.

We humans are relative late comers. Insects, birds, fish, flowers as well as other colorful animals have been around far longer than we have. They obviously see and use color and have been doing so for millions of years.
Therefore human perception has nothing to do with color being intrinsic or not.

But is it really an intrinsic property of the world? Again, as other posters in this thread have noted, is a color not just an invention by the brain used to differentiate between varying wavelengths?

I believe that this is simply confusing an effect with its cause. They are describing the physics behind color transmission and detection not the why of or cause of it. Why does and object absorb photons of various wavelengths except one? Because that is its color and that is the way that its color is transmitted.

Again, not necessary. Roses could just have developed in a way that its petals are constituted of particles that would absorb and reflect the necessary wavelengths to produce the impression of the color rose in our minds. The reason then which would explain why roses would not have a distinct 'blue' gene is that the constituents of the petals would all have to change in order for the wavelengths of light to be absorbed and reflected back to create the color blue.

Again this is the way not the why. Why souled a plant have a color gene at all; why should its petals be made up in such a way as to reflect one particular wave length, if not because of color, its intrinsic color, and why would animals develop the ability to detect and perceive these different wave lengths unless it was an already existing characteristic of its environment. Roses did not read our minds and respond genetically to our strictly mental perceptions.
Its true that we gave the different colors different names and developed pigments and dyes of the same colors we saw in nature but they were there and we perceived them long be for we developed language and chemistry, long before hominids were even on this colorful world.
Its also true that we detect photons of different wavelengths and that these photons are generated and emitted by elect ons and that their wavelength is determined by the energy state of the emitting electrons; but, as I said, the photon does not have any characteristic wavelength of its own and is only a carrier of information, a messenger particle of the electromagnetic force. It is the objects that emit and/or reflect them that give them the characteristic that we call color. It is the color of the object that causes certain photons to be reflected and other absorbed.

Gold Member
Digressing a little, I've read that left and right handedness is similarly a mental construct, does this idea hold any water?

Staff Emeritus
Gold Member
fi said:
Digressing a little, I've read that left and right handedness is similarly a mental construct, does this idea hold any water?

That's an awfully big digression from this topic. If you'd like to discuss this question, please do so in a new thread.

gerben
Royce said:
It is the color of the object that causes certain photons to be reflected and other absorbed.

No, it is the chemical composition that determines this.

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Royce
gerben said:
No, it is the chemical composition that determines this.

This and the other posts by hypnagogue and zoobyshoe are perfect examples of reducing a common phenomenon to physics and losing sight of the actual cause or reason why by concentrating on the how.
Yes, it is the chemical composition and structure of reflecting body that determines the wavelength of the reflected photons, but what is it that determines the chemical composition of the body such as a flower petal?
It is the color of the petal determined by the flowers genes, or it is the pigment choosen by the painter etc.
It is clear and varifiable that we all see and perceive the same colors under the same conditions. This is true or Hypnogogue's link would not make any sense to some of us. If this is a common human trait, there must be a reason for it. It must have some survival advantage. Yet this is perception not color.
Our eyes still see, detect, the same true color as long as the light source is bright enough. This is proven when we we put the mask in place and see that the colors and shades are the same.
Our perceptions do not change the actual color of the light striking our eyes. The determining factor is the color of the object seen which determines the wavelength of the light. It is a scientific fact, by definition and observation, that certain wavelengths of light are consistantly specific corresponding colors and each color has its own characteristics of propagation, energy etc.

Staff Emeritus
Gold Member
Royce said:
This and the other posts by hypnagogue and zoobyshoe are perfect examples of reducing a common phenomenon to physics and losing sight of the actual cause or reason why by concentrating on the how.

What exactly is being overlooked?

Royce said:
Yes, it is the chemical composition and structure of reflecting body that determines the wavelength of the reflected photons, but what is it that determines the chemical composition of the body such as a flower petal?

Genetics and environment determine the flower's physical makeup, clearly. To say that color causes chemical composition is so backwards that I don't know where to start addressing it.

Actually, here's a start. Define "color."

Royce said:
It is clear and varifiable that we all see and perceive the same colors under the same conditions.

That is a reasonable assumption, but ultimately it is not verifiable. I cannot peer into your mind and see what you see. I can only guess at what you see based on various empirical clues and assumptions.

Royce said:
This is true or Hypnogogue's link would not make any sense to some of us.

This claim is not at all obvious. Nonetheless, I won't press the issue because the claim that we essentially perceive the same colors is a reasonable one, and we shouldn't complicate the discussion any more than we need to.

Royce said:
If this is a common human trait, there must be a reason for it. It must have some survival advantage.

Is there a survival advantage for seeing blue instead of blue? I tend to doubt it.

Regardless, a simple explanation for why we perceive the same colors is simply that our common genetics endows us with similar brain structures with which to process visual information, and so it follows that we see similar colors. Why do males have nipples? Survival advantage? It's probably just because males have some portion of the genetic code in common with females.

Royce said:
Our eyes still see, detect, the same true color as long as the light source is bright enough. This is proven when we we put the mask in place and see that the colors and shades are the same.

Using the mask does not change the brightness of the visual stimulus. All physical properties of the stimulus remain constant. The only change is the surrounding context. This very strongly suggests that the perceived color is a function of brain processing rather than the stimulus itself.

Royce said:
Our perceptions do not change the actual color of the light striking our eyes. The determining factor is the color of the object seen which determines the wavelength of the light.

Color determines light's wavelength? Unless you're using "color" as some baroque codename for some other physical process that normally doesn't go by that name, or using some strange sense of the word "determines," this claim is just wrong. Where is the entity in physics called "color" that determines light wavelength?

Royce said:
It is a scientific fact, by definition and observation, that certain wavelengths of light are consistantly specific corresponding colors and each color has its own characteristics of propagation, energy etc.

Actually, it is a scientific fact that any given wavelength of light can be perceived as a large range of colors depending on various conditions and contexts. Once again, this very strongly undermines the thesis that color is something that inheres to the stimulus itself.

Royce
hypnagogue said:
What exactly is being overlooked?

The cause, the why, the particular chemical composition or structure is where it is and why it is a genetic trait. I say because it is the physical way in which color is transmitted. A red flower is one composition while a white is another. Color is the cause or why. the other is the how.

Genetics and environment determine the flower's physical makeup, clearly. To say that color causes chemical composition is so backwards that I don't know where to start addressing it.

I did not say color causes chem. comp. I said that the chem. comp is the way that it is so that its characteristic color is reflected. Ask why there should be genes that make this particuar composition that consistantly reflects a certain color of light in effect giving the flower that color and different set of genes for another color.

Actually, here's a start. Define "color."

Hue. Try to define taste or feel.

That is a reasonable assumption, but ultimately it is not verifiable. I cannot peer into your mind and see what you see. I can only guess at what you see based on various empirical clues and assumptions...This claim is not at all obvious. Nonetheless, I won't press the issue because the claim that we essentially perceive the same colors is a reasonable one, and we shouldn't complicate the discussion any more than we need to.

We can show a number of people a swatch of color and have them point out the same color on a color chart or wheel. Not only will they closely agree with each other and us but they will agree with the technical definition of that color. What color that they actually may experience doesn't matter and is impossible to determine so long as we all agree that the colors are the same.

Is there a survival advantage for seeing blue instead of blue? I tend to doubt it....Regardless, a simple explanation for why we perceive the same colors is simply that our common genetics endows us with similar brain structures with which to process visual information, and so it follows that we see similar colors. Why do males have nipples? Survival advantage? It's probably just because males have some portion of the genetic code in common with females.

I can think of a number of possibilities. The first to come to mind is that we are descended from hominids that were both hunters and hunted and it was important that we be able to discern color contrasts in differing light levels.
It was more important that we see the contrasts than the actual real colors because of the camouflage used by the animals hunting us and the ones that we hunted.

Using the mask does not change the brightness of the visual stimulus. All physical properties of the stimulus remain constant. The only change is the surrounding context. This very strongly suggests that the perceived color is a function of brain processing rather than the stimulus itself.

No, it changes nothing except it hides the contrasting area around it.
The fact that it appears brighter or darker in areas of changing contrast or light levels is a function of our brains, perception, not our eyes, sight. Why do we do this and why is it nearly universal? I don't know but speculate as I did above.

Color determines light's wavelength? Unless you're using "color" as some baroque codename for some other physical process that normally doesn't go by that name, or using some strange sense of the word "determines," this claim is just wrong. Where is the entity in physics called "color" that determines light wavelength?

I said that the color of an object determines which wavelengths of light is reflected. I also said that certain wavelengths of light are defined as certain colors. There are thousands of technical, scientific and artistic charts of the visual spectrum which show these definitions whether the light is reflected or emitted.

Actually, it is a scientific fact that any given wavelength of light can be perceived as a large range of colors depending on various conditions and contexts. Once again, this very strongly undermines the thesis that color is something that inheres to the stimulus itself.

This is why I continually specified under the same lighting levels or conditions. Again this is perception and not seeing or color transmission.
Given adequate light levels our eyes see and detect the same colors regardless of our perception.

zoobyshoe
Excerpt from The Case of the Colorblind Painter

"Mr. I could hardly bear the changed appearances of people (like animated grey statues') anymore than he could bear his own appearance in the mirror: he shunned social intercourse and found sexual intercourse impossible. He saw people's flesh, his wife's flesh, his own flesh, as an abhorrent grey: flesh-colored' now appeared rat-colored' to him. This was so even when he closed his eyes, for his vivid visual imagery was preserved but was now without color as well.

"The wrongness' of everything was disturbing, even disgusting, and applied to every circumstance of his daily life. He found foods disgusting due to their greyish, dead appearance and had to close his eyes to eat. But this did not help very much, for the mental image of a tomato was as black as its appearance. Thus, unable to rectify even the inner image, the idea, of various foods, he turned increasingly to black and white foods - to black olives and white rice, black coffee and yoghurt. These at least appeared relatively normal, whereas most foods, normally colored, now appeared horribly abnormal. His own brown dog looked so strange to him now that he even considered getting a Dalmation...

"As the months went by, he particulaly missed the brilliant colors of spring - he had always loved flowers, but now he could only distinguish them by shape or smell. The blue jays were brilliant no longer; their blue curiously, was now seen as pale grey. He could no longer see the clouds in the sky, their whiteness, or off-whiteness as he saw them, being scarcely distinguishable from the azure, which seemed bleached to a pale grey. red and green peppers were also indistinguishable, bu this was becuse both appeared black. Yellows and blues, to him, were almost white."

An Anthropologist On Mars
Oliver Sacks, Vintage Books, 1995, pp. 7-9

nameless
Actually, here's a start. Define "color."

I would describe 'color' as;
the mind's interpertation of specifically coded 'information' that the 'eye' transmits from the colapsed quantons (information/probability/possibility waves a.k.a. Mind) to the brain..
Other senses can also perceive this programming.
There is nothing like a 'color-thing' actually out there! Just 'program code' from the collapsed waves, via sensory 'perception' to the 'central processing unit' (CPU), the 'brain/mind' to convert and manifest into our concepts of the 'material' omniverse.

On second thought, perhaps this 'definition' would apply to the entire apparent panoply of manifested omniversal phenomena.

Just another perspective, offered for it's apparent rarity, for what it's worth...

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octelcogopod
Royce, I understand exactly what you mean though.
In some odd way, how can something as beautiful as the world be just a coincidence?
How can the perception of light be just that, a relative perception?
Are we the only ones seeing the world this way?

I mean why does color even exist? Why do we perceive color?
A human could function perfectly fine without it.
Why do waves have different frequencies?
Why are these frequencies even perceived as color by the brain?
Just what IS a color anyway?

I mean this can be deducted in a number of ways.
We don't really know why the universe exists, nor do we know exactly why the forces exist, like electromagnetism or gravity.
They just exist, for some unknown reason.
Could it be, that you as a human, is interjecting more value into the discussion, that is originally there?
Trying to understand "why" the universe is the way it is, on an abstract level, is not possible.

That was a bit off topic, but to my point:
It could be that we evolved to perceive light frequencies, simply because they were there.
Maybe some animals even started perceiving in black and white, but then as they become more and more evolved, they perceive more and more of the universes qualities.

I hope I didn't go too off topic, and I hope that I understood royce's point.