What is Colour: Definition and 178 Discussions

Color (North American English), or colour (Commonwealth English), is the characteristic of visual perception described through color categories, with names such as red, orange, yellow, green, blue, or purple. This perception of color derives from the stimulation of photoreceptor cells (in particular cone cells in the human eye and other vertebrate eyes) by electromagnetic radiation (in the visible spectrum in the case of humans). Color categories and physical specifications of color are associated with objects through the wavelengths of the light that is reflected from them and their intensities. This reflection is governed by the object's physical properties such as light absorption, emission spectra, etc.
By defining a color space, colors can be identified numerically by coordinates, which in 1931 were also named in global agreement with internationally agreed color names like mentioned above (red, orange, etc.) by the International Commission on Illumination. The RGB color space for instance is a color space corresponding to human trichromacy and to the three cone cell types that respond to three bands of light: long wavelengths, peaking near 564–580 nm (red); medium-wavelength, peaking near 534–545 nm (green); and short-wavelength light, near 420–440 nm (blue). There may also be more than three color dimensions in other color spaces, such as in the CMYK color model, wherein one of the dimensions relates to a color's colorfulness).
The photo-receptivity of the "eyes" of other species also varies considerably from that of humans and so results in correspondingly different color perceptions that cannot readily be compared to one another. Honey bees and bumblebees have trichromatic color vision sensitive to ultraviolet but insensitive to red. Papilio butterflies possess six types of photoreceptors and may have pentachromatic vision. The most complex color vision system in the animal kingdom has been found in stomatopods (such as the mantis shrimp) with up to 12 spectral receptor types thought to work as multiple dichromatic units.The science of color is sometimes called chromatics, colorimetry, or simply color science. It includes the study of the perception of color by the human eye and brain, the origin of color in materials, color theory in art, and the physics of electromagnetic radiation in the visible range (that is, what is commonly referred to simply as light).

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  1. brotherbobby

    LaTeX 1. Colour while using ##\LaTeX## 2. Preview first time

    I have observed that one cannot use colour here while typing something in ##\LaTeX##. Let me try : ##\text{Let's see if this can be \color{blue} {coloured}?}##. Nope, I type, via an edit after posting. Of course I can use colour from the panel above, but that will have to work for the entire...
  2. Astronuc

    BBC - Our eyes can change colour in surprising ways

    Our eye colour doesn't always remain constant throughout our lives – in fact, a wide range of external influences can change it, from injury to infection and sun damage. And sometimes the change appears to happen spontaneously...
  3. Supershandy

    I Help with Kubelka Munk equations in Excel

    Hello everyone. I'm trying to do a Kubelka Munk equation for paint samples and would like to do the calculation in Excel first before moving it over to a programming language outside of MATLAB. I have Spectroscopic scans of the samples and put them into a database where the K/S values have been...
  4. V

    A Extracting Color from a Spectral Date

    Hello everybody, I would love some help on the following; I have a spectral date (As image 1 below) formed by the wavelength, refraction index and the absorption coefficient. Is there any way to relate this spectral date to a dominant wavelength? or in a few words extract the color from this...
  5. mcastillo356

    Edit: how to colour an edited formula

    Hi PF How to colour the edited formula? Greetings!
  6. DaveC426913

    How can I effectively display different types of worker coverage on a map?

    OK, I'm stuck on a problem implementing this map. (It'll be built in HTML with JavaScript and CSS and is interactive but that's just context - this is really about map-colouring.) The function of the map is to help users see at-a-glance what regions/counties of the province are serviced by...
  7. P

    Does the colour of a container affect how fast water in it cools?

    Containers are painted with the 7 colours of the rainbow; each colour corresponds to a different wavelength. Pour boiling water into each container. Which container would cool the fastest? Does the result change depending on whether the exterior or the interior or both are painted? The material...
  8. DaveC426913

    Solving a colour puzzle programmatically

    Just for fun (read as: staring at the ceiling trying to sleep), trying to figure out if there is a programmatic way to solve this colour-matching puzzle app on my phone. It's called... Here is a partially solved puzzle: The dotted tiles are immovable, and serve as references. The undotted...
  9. N

    I Blackbody colour of metals versus stars

    Hello. I am new to this forum and joined because I am at home nerding out trying to work something out. Why do white hot metals seem to be much cooler than white hot stars. The attached picture is from Wikipedia relating temperature of a hot metal to its temperature. For example a red giant...
  10. N

    What is salt that has a green colour?

    What are salt that have green colour?
  11. P

    I Observing colour through telescopes

    Excluding planets and given normal dark skies, what minimum aperture size of a (non-refractor) telescope is required to just start getting hints of colour in deep sky objects like nebulae and galaxies? I mean in real time, unaided eye, no photography.
  12. PeroK

    I Are Hadrons and Gluons Symmetric Against Interchange of Colours?

    This is from Griffiths' Elementary Particles, section 8.4.1. By analysing the colour factor, the conclusion is that a quark/anti-quark pair attract in the colour singlet configuration: $$\frac 1 {\sqrt 3}(r\bar r + b \bar b + g \bar g)$$ And this explains (to some extent) why mesons are...
  13. S

    Wavelength of the red colour of this helium discharge tube

    Red has the longest wavelength compared to the two other colours so the location of red will be at point C. x = 11.5 cm L = 30 cm d = 1870 nm Putting all into the formula, I get λ = 717 nm Where is my msitake? Thanks
  14. weningth

    A How to deal with colour indices on spinors

    I want to calculate transition amplitudes in QCD for processes like ##q(k)q^\prime(p)\rightarrow q(k^\prime)q^\prime(p^\prime)##, where ##q,q^\prime## are quarks. However, I am unsure what to do with the colour indices of the quark spinors upon squaring the matrix element. For the sake of...
  15. DennisN

    WW2 - D-Day - Real Footage in Colour

    Intense, dramatic, fantastic and at the same time terrible. A must see for history buffs, I'd say. WW2 - D-Day. Invasion of Normandy [Real Footage in Colour]
  16. D

    I The Shadow Of An Atom - False Colour Images Reveal Structure

    I've been adding some renderings I did of the M87 black hole on a different thread and was asked to elaborate on the source of this technique which was investigating images of the shadow of an atom. You can look up the original experiment on Google, as well as observe the final image. The...
  17. ThomOnTheBus

    Optical effect seen on a bus: mirrored screen shows different colors

    Hello Physics People, i was on bus 59 lately and i noticed a typical optical effect. There is a monitor/screen in the front of the bus that lists the current and coming stops and updates when you pass one. Its colour scheme is was blue/lightblue/white (see first picture). But when i looked at...
  18. K

    B Additive colour theory and "traditional" colour mixing

    Hi folks. I am trying to reconcile the additive colour theory of light with more traditional grade school colour mixing. For example, we all know that blue paint plus yellow paint makes green paint. How do we explain this from the perspective of light? So the yellow paint appears yellow because...
  19. Delta2

    B Mars Water: The Truth Behind Its Blue Color and Recent Discovery Revealed

    I guess water in Earth , in big lakes or seas, looks blue because the Earth's sky is blue and the water's surface reflects the sky. Now if there would be some big lake of water at Mars, how the water surface colour would be? I guess the colour of Mar's sky which is red (right or wrong?) It is...
  20. Beanyboy

    Exploring the Relationship Between Color and Temperature in Thermal Measurements

    There's a passage in Kumar's (excellent) book, "Quantum", which has me confused. He notes that Planck is aware that as the temperature of a heated poker rises, the colours change from red through to bluish white. Later in the passage, he refers to Herschel's earlier work on the relationship...
  21. Wrichik Basu

    What Role Do Cone Cells and Iodopsin Play in Colour Vision?

    As per Wikipedia, there are three types of cone cells. Quoting Wikipedia: I searched a bit more, and found that there are three different types of iodopsin pigment in these cells. Quoting Wikipedia again: Can you say what reaction occurs for each of the pigments when they are exposed to...
  22. PumpkinCougar95

    B Do Electrons Get Excited and De-Excited Equally in Colored Compounds?

    I am not able to understand why compounds have colour. I have read that it is due to excitation of electrons from one atomic/Molecular orbital to another because of which certain wavelengths are absorbed, And we can see the "complementary colour" of those wavelengths. What I don't understand is...
  23. C

    Can light be split by colour accurately?

    Dear Physicists, My understanding of physics is at the utmost basic level. Let me apologise in advance for what is probably a dumb question. What I do know (I think): When white light hits a prism, it comes through the other side, showing the colours of the rainbow. It is my udnerstand that...
  24. T

    I Window blinds - colour depends on window open/closed

    Hello, I am a bit confused regarding something I have observed on the blinds in front of my windows. The "real" colour is a sort of a light brownish colour (NCS S 4010 Y50R to be precise - see http://ncscolour.com/product/s-4010-y50r/). However, when the window in front of it is closed, the...
  25. navneet9431

    Is light eye colour dominant or recessive trait?

    Homework Statement A study found that children with light-coloured eyes are likely to have parents with light-coloured eyes. On this basis, can we say anything about whether the light eye colour trait is dominant or recessive? Why or why not? Homework Equations Not Any The Attempt at a Solution...
  26. heavystray

    B Why Do We Use Different Pairs of Filters to Determine the Temperature of Stars?

    Hi, in determining the temperature of stars using colour index (U-B,B-V,V-R, etc), why do we need to use the appropriate pairs of filters based on their range of temperature? (this is what i read from wiki) For cool stars, we use R-I, and for hotter stars, we use B-V. I don't understand how...
  27. heavystray

    B Temperature based on colour index using Planck's law

    Hi, I'm trying to find temperature of stars using the stars' B-V magnitude by using the Planck law. However i do not know how to solve for T (assume other quantities are all given and determined first). Any idea how to do so? I already tried to do it but reach a dead end. Here I attached the...
  28. R

    B Understanding Black Body Radiation and the Sun's Color Temperature

    So, if frequency(max) of light emitted from an object proportional to temperature in kelvin, how can sun have max frequency around the yellow region while blue flames are much less hot?
  29. Pushoam

    We see colour of an object due to reflection of light.

    Homework Statement How to demonstrate that we see colour of an object due to reflection of light? Homework EquationsThe Attempt at a Solution We see an object because photons from that object come to our eyes. The photons from the object comes to us due to radiation or reflection. If the...
  30. Zaya Bell

    Campton Scattering: Colour Change Explained

    Colour is defined by frequency/wavelength. Hence whenever they both change, we are to observe a change in colour. But that isn't the case for campton scattering. Or is it?
  31. shihab-kol

    What Is the Nature of Black in the Visible Spectrum VIBGYOR?

    In the visible spectrum VIBGYOR, there is no black colour.So, what do we percieve as 'black' ? Another of my queries is that when dispersion takes place there is a change in wavelength but not so in case of frequency. But they are related inversely. So, why does this happen?
  32. Zaya Bell

    B Colour Change Problem: Does Wavelength Affect Colour?

    Whenerver a monochromatic light, say red changes medium, it reduces in speed which in turn reduces wavelength. But then if wavelength is reduced should not the colour change? Or dies it?
  33. bruha

    I Colour star versus temperature

    Hello I am interested about correlation between star surface temperature and its visioned colour ,for example orange red Arctur has surf temperature cca 4300 K ..but comparing to for example hot piece of metal? its temperature 2000 K respond white colour. ? What is a matter of this disagreemet...
  34. C

    Why are prescription drugs mostly white in colour?

    Am I imagining it? Is there something in common about the structure of substances that interact with human biology which means they tend to be white? Do medication manufacturers just somehow artificially whiten them to meet consumer expectations? Thanks for any input.
  35. C

    I A few questions about colour in QCD....

    I was watching some new lectures on QCD from Colorado and I have a few questions from what I heard - --The ##\lambda^a_{ij}## are generators of SU(3) in the fundamental representation so are 3x3 matrices. That is because the ij indices are colour indices and they act on a 3x1 vector in colour...
  36. L

    B Do atoms give off radiation that determines the colour?

    Do atoms give off radiation that determines the colour? I want to understand this, please give me explanation.
  37. SWFvanRijk

    A Are Mesons in Colour Singlet State?

    I read that hadrons are in colour singlet state and that gluons are not and that the colour singlet gluon is forbidden for the reason of making strong force a long range force otherwise (and that SU(3) has 8 generators and thus 8 gluons) but my question is: are mesons in a colour singlet state...
  38. G

    Why are mammals limited in color compared to other animals?

    How come mammals are so "drab", compared to what is typically seen in the other major animal taxa? In a bit more detail, what I mean is this: The feathers of birds, the skins of amphibians, the scales of reptiles and fish, the carapaces of insects and spiders, all of those seem to fundamentally...
  39. S

    Which Skin Colour Distribution Map is Most Reliable?

    I see 2 commonly quoted maps for distribution of native human skin colour. Both are old; they have a lot of odd divergences - as well as many matching features, some of which are hard to explain. One is Biasutti, 1940: https://upload.wikimedia.org/wikipedia/commons/8/81/Map_of_skin_hue_equi.png...
  40. Superposed_Cat

    What causes paint to change colour over time?

    What compounds,reactions and factors cause modern day paint to change hue intensity over time? Any help appreciated.
  41. S

    What color is the sky from space for an astronaut?

    suppose there is an astronaut sitting in a space station orbiting Earth, what colour would the sky appear to him? Same as us? Why or why not? Thanks!
  42. 24forChromium

    What determines the colour of chromium compounds?

    I am aware of the processes through which cations are coloured in ligand complex (splitting of incomplete d-shell will absorb specific frequencies of the spectrum). However, I am only aware of this interaction with aqueous mono-atomic cations, which is not always a present condition when colours...
  43. piJohn1411

    Mathematica Is it possible to colour the rows or columns of a matrix?

    Hi, I was wondering if it's possible to colour the rows and columns of a matrix in mathematica. I have received help from another forum and the code of my matrix is the following: Rasterize@ Style[MatrixForm[{{n, -1 + n, -2 + n, \[CenterEllipsis], 1}, {2 n, 2 n - 1, 2 n - 2...
  44. Rishi Gangadhar

    What decides the colour of light?

    Consider a beam of light passing through a slab of some refractive index. We know that the speed and wavelength of the light changes, but its frequency remains the same. Since the wavelength of the light changes, does its colour change, or does it remain the same as its frequency remains the same.
  45. A

    Can some bright spark help me? Colour of Light vs Time

    I'm writing a Science Fiction story which has one place where time runs at normal speed, and another place next to it, where time runs at a much slower speed. If you stand in the normal place and look into the slow place, you will see people moving around as if in slow motion. But what would...
  46. S

    I Can Black Holes Have Equal Spin and Behave as Indistinguishable Fermions?

    Well, do they? Also: black holes, unlike elementary particles, have continuous distribution of rest mass, because they are free to absorb photons and gravitons of arbitrary mass, and kinetic energy of particles they capture. If two Kerr or Newman black holes have equal spin, which happens to be...
  47. Suraj M

    Probability of a colour blind grandson

    Homework Statement Here is the question as it is. A colour blind man marries a woman with normal sight who has no history of colour blindness in her family. What is the probability of their grandson being colour blind? (1) 0.25 (2) 0.5 (3) 1 (4) Nil Homework Equations -- The Attempt at a...
  48. J

    What is the Concept of Colour Force in Quantum Physics?

    < Mentor Note -- OP has been reminded that he needs to show more effort in his thread starts in the future... > what is colour force
  49. H

    I saw a Violin change the colour of a liquid,I don't know how

    I've been looking around and I saw that chemicals are involved and they apparently played in the key of B major, if that helps. Oh also someone mentioned there may be oil at the top. Does anyone know how this happens or have even seen this? I know sound is pressure, and it goes through things...
  50. Puma

    Best colour to make paint UV resistant

    Hi I am looking to repaint my windows. I've noticed that black paint lasts very well generally. I don't really want my windows black. Is there anyway I can reduce uv damage to the binder in the paint by adding some UV blocking colour? I've googled UV blocking pigments but it doesn't seem to come...