What is Color: Definition and 503 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. N

    Colour depends on wavelength or frequency?

    This is the Question: It's from the book: Concepts of Physics by Dr. H C Verma. The common observation is off course that a red light would appear red even when viewed from under the water (for eg in a swimming pool). But, in the same book, it's been written that colour depends on wavelength...
  2. SamBiswas95

    If 95% of the atmosphere was SO2, how would the sky look?

    Taking into account the Rayleigh scattering phenomenon, assuming that the atmosphere is 1 bar, how would the light from the G2V-type star interact with this kind of environment? Could the colour of the sky even alter despite the fact that there is a significant amount of sulfur dioxide in the...
  3. nomadreid

    (Solved) Change fill-in color in PDF file with Adobe without Pro

    I don't have a color printer, so the standard blue used by Adobe for fillable forms don't come out well. Going to Edit>Text , Adobe gives me an ad to upgrade to Pro. Various internet sites tell me to go to form field settings or to Preferences, but I cannot find a path that will get me there. Is...
  4. ruxy667

    Automotive What does the smoke color means in diesel car and petrol car?

    Hi there, i just started to learn mechanic about few years ago and I wanted to know about car smoke color, What does the smoke color means in disel car and petrol car, Black,Blue,Grey,White smoke color?
  5. J

    How Does Flickered Light Affect Our Brain's Perceived Contrast and Brightness of Images?

    Bear with me this will be long, but everything here I feel is necessary to understand the context. I recently used a crt at varying refresh rates and noticed a few things that has made me question how the brain perceives colors on a display. First, is that my crt appears to have more color...
  6. T

    I The Science Behind Rainbows: Explaining the Center of a Rainbow | Gooood Morning

    Gooood Morning I was traveling with my son and he noted the rainbow out the window and asked why we see only half. I informed him that the earth blocks the other half and if we were in an airplane, we could see the entire circle. Set that aside. When we look at the electromagnetic spectrum...
  7. Z

    Aromatic amines having a brown color

    Aromatic amines having a brown color
  8. M

    Microsoft Excel background grid color default reverts

    Basically, microsoft excel always has white background cells, and I'd like it to be a different color. Here's what I've tried: I configured the below registry value in my Windows 11 user profile to change the default window color from 255 255 255 (i.e. white) to 192 192 192 (i.e. a not so...
  9. A

    B Color of a mirror on the Earth

    If I place a mirror on the ground facing upward, what color will those who observe it from space see?
  10. M

    I Investigating a 3D Color Hue Phenomenon with Blender and Just Color Picker

    I have been doing some 3D computer graphics modelling and I have observed a phenomenon I cannot find anything about. I am using Blender (free 3D program). I am also using "Just Color Picker" which is a free Windows tool that let's you check the hue/saturation/value (HSV) for any color on your...
  11. A

    I What Causes the Darkening of Metal Bucket Color at High Temperatures?

    This is the color of the metal bucket when it's not hot. But whenever it is hot, the red changes to dark, and then back to red again when it is not hot. See the following youtube where I just threw the fake money at the bucket (see background below). Can you explain how the phenomenon work...
  12. R

    B Is it possible to get the photoelectric effect in red color frequency?

    Is it possible to get the photoelectric effect in red color frequency?
  13. Salmone

    I Rayleigh scattering -- What is the true reason for the color of the sky?

    I have a little question about Rayleigh scattering: I know that Rayleigh cross section is proportional to the inverse of the fourth power of the wavelenght of the incident light and that it is so even the intensity of the scattered beam of light, now: 1. What is the color of the sky due to...
  14. N

    Metamerism (vector-matrix representation of color perception)

    For the illuminant A for the illuminant B Did I got them correct? Thank you
  15. shivajikobardan

    MHB Why do we use CMYK color for printing?

    I will tell my research that i have done earlier here. CMYK is used for print pieces like brochurers and business cards. For RGB we need to start on black paper but we can't add light until we reach white because light can't be painted on surface, what does this bold content means to say? in a...
  16. shivajikobardan

    Comp Sci Why do we use CMYK color for printing?

    I will tell my research that i have done earlier here. CMYK is used for print pieces like brochurers and business cards. For RGB we need to start on black paper but we can't add light until we reach white because light can't be painted on surface, what does this bold content means to say? in a...
  17. Kyran

    B Why are things the color they are?

    I have not noticed anything in common between all things that are the same color. It must be something on the atomic level but if I look at the periodic table I see no pattern in how things behave and what their color is. So how can the sun be the same color as a highlighter and plastic the same...
  18. 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...
  19. jaumzaum

    I Color Theory - What does blue + yellow make?

    Hello! PS. This is not a Homework question, I am asking about a concept. I am a Physics teacher from Brazil and last week one of the biggest Engineer universities here applied its entrance exam. However, a lot of teachers (including me) don't agree with one of the answers. Can you guys help...
  20. I

    Cable color standards in the US

    I am from Europe and mainly do engineering here but now I have a new project for a machine that is going to be installed on a wind-farm outside of New York. We have a very specific customer spec that specifies the wire colors that we have to use in all the power cables. The spec says the...
  21. M

    MHB Counting Color Combinations in 12 Triangles

    There are 12 triangles (picture). We color each side of the triangle in red, green or blue. Among the $3^{24}$ possible colorings, how many have the property that every triangle has one edge of each color?
  22. jk22

    Medical Color of eyes : mutation due to evolution or racial selection?

    If different eyes appeared let say to less sun or an accidental mutation, has it become subject to selection of individuals like eugenism or due to modern gene technology nowadays ?
  23. meher4real

    Finding Color of Two Lights Given Slit Source & Screen Distance

    Given values : - Distance between the slit source and the screen L - d1,d2 The problem is to detemine the color of the two lights
  24. Doctor U

    Exploring the Possibilities of Sky Color

    As far as I know, the sky is blue because of the natural vibration of the molecules of the air enter in a ressonance with the ultraviolet spectrum, so when the sun light hits the air molecules the scattering occours more on the ultraviolet part, but blue part of the visible spectrum is more...
  25. J

    Need a "keyboard shortcut" to change selected text's "text color" in G

    I use the GMail web interface, in Firefox, for all my email needs. 
 I frequently change the color of text that I quoted from the Sender in my GMail replies. 
 You wrote, ". . . a;sdkfjasl;fkjasl;kfj . . . ," 
 and I just want to...
  26. S

    Can a diamond's color be simulated by only a surface coloring?

    I was reading this article about the a replica of the famous Hope Diamond and its antecedents: https://www.nytimes.com/2020/11/28/style/hope-diamond-story-smithsonian-copy.html This part seems to say that the color is to be simulated by a coating: It would seem to me that the proper attenuation...
  27. J

    Who is a Physicist and Color Scientist with Experience at Kodak and Pantone?

    Physicist and color scientist. Experience at Kodak and Pantone. Taught physics at community colleges in retirement.
  28. J

    What do the different colors of plasma in spark gaps mean?

    Hi, I am looking at videos of spark gaps and see that there are different colors of plasma. I really should've been a physicist because this may be fundamental, but I'm wondering what the different colors mean? I have seen purple and white. My guess is that white is a higher energy discharge...
  29. mcastillo356

    LaTeX How to change the text color with LaTex

    Isn't it $$\color{red}x\color{black}y$$
  30. S

    B The Physics of Color Perception

    When you look at the following image through a prism with the apex (thinner portion) pointed towards the left or the right, why do you see magenta on one side and green and black on the other? Keep in mind that the spectrum is reversed.
  31. G

    I My 50 year old Science book says that Black is the absence of all color

    My 50 year old science book says, black is absence of all color. Do any books still say, black is absence of all color? I looked online for 30 minutes no where say, black is absence of all color. NOW everything says, Black is the darkest color. Why the change in books? If black is not a...
  32. P

    Rayleigh Scattering Conceptual Question about the Color of the Sky

    We know ##\lambda_{blue} < \lambda_{red}## so citing the formula above (in the relevant equations) it's apparent that blue light is scattered more than red light. But presumably this would hold for ##\theta = 0## as well but when we look at the sun head on we don't see blue, we see red/orange...
  33. sekushi0range

    Reason for Ferroin's color shift

    Ferroin is a redox indicator. It is the complexation of phenanthroline and iron. In its reduced state the Fe (II) - phenanthroline complex is red and in its oxidized state the Fe(III)- phenanthroline complex is blue. I am trying to understand in the context of d-d orbital transitions why this is...
  34. F

    Best outside color for thermal insulation

    I'm wondering if the outside color has an influence on the thermal depletion of things such as a thermos, a wall, etc. Assuming, obviously, there's no sunlight hitting on them. It certainly has, but what difference percentage can we typically expect for example for bottles such as the ones on...
  35. A

    I Help with the color of a star cluster

    I am working on a problem which asks for the B-V magnitude of a star cluster given N stars of type F and M stars of type K. I have values for B-V for both stellar types. I've derived a general formula for computing the magnitude of the cluster from the magnitudes of each star type, which...
  36. N

    I Color state of quarks in quark-gluon plasma

    Hi, I have been taught that quarks don't exist individually on their own, as they has with be with at least another antiquark to form a colorless state. But in the quark-gluon plasma, do we have individual quarks in a color state or do they still, somehow, are in a color-neutral state? Thanks!
  37. S

    Text color detection algorithm giving pixels of text

    I'm creating a type of image processing software and I have a need to get the color that best represents text once I have identified the pixels in a region of text. I've tried using simple strategies like "averaging" the pixels or taking the most common pixel, but these produces bad results An...
  38. A

    B MRI vs Color X-Ray Technology: What Are the Differences and Benefits?

    Today I read about a seemingly new way of using Xrays that results in images that can be colored and more detailed. https://www.marsbioimaging.com/mars/ See this link for example. I do wonder what would be the major differences or benefits from such technology given modern MRI also has very...
  39. X

    B Hypersonic aircraft shock layer color

    As a lot of people know, when things go hypersonic or even orbital velocities in the atmosphere, it’s going to get hot, scorching hot. The air emits black body radiation that are at the red spectrum (around 2000 to 3000 kelvins) sometimes goes yellow (5000-8000 kelvins maybe?) at re-entry...
  40. K

    Color Index and Intrinsic Magnitude of a Star

    I first determined ##E_{U - B}## by using the second equation listed above: $$U - B = (U - B)_0 + E_{U - B}$$ $$8.15 - 8.50 = -0.45 + E_{U - B}$$ Then since the ratio to the B-V color excess is known, I solved for that and obtained ##E_{B - V} = 0.14##. Using the ratio of total to selective...
  41. DrClaude

    Cool video on Color perception

    There are been many threads at PF on the perception of color. I would like to share a good video on the subject, which contains many interesting visual effects. This is from the Technology Connections channel, which has many videos of interest to our community. I encourage you to browse around.
  42. W

    I How electrons absorb or emit photons

    Hi, I am aware that the reason why objects have color is an old subject. However I come across two claims which sound like they are in contrast to each other. On one hand I read that the photons with specific frequency in incoming light are absorbed (i.e. have enough energy to move an electron...
  43. L

    What Color Will NIR Laser Goggles Be?

    Colors come about because the wavelength is reflected off the object while the rest is absorbed. So orange looks orange because the orange is reflected while rest absorbed. For laser goggles that is rated for say 532nm (green wavelength). It must absorb the 532nm and so the reflected color...
  44. V

    MHB Number of ways to color a grid

    Hello, Kindly, can anyone solve the following: How many combinations: 8 colors, which each can be used twice in the following grid 1 3 5 7 2 4 6 8 where a color can only appear like this 1 with 5 3 with 7 2 with 6 4 with 8 So, non-valid combinations would be 1 with 2 1 with 3 2 with 3...
  45. Manasan3010

    I Exploring the Physics of Photoelectric Cells: Electrons, Energy & Color

    In this article, writer says that when atom is hit by photon it gets excited and expelled out of atom and this can be used to form images. My questions are: Why didn't the electrons get to a higher energy level, instead of getting knocked out? How do we find the color(frequency of wave) using...
  46. Sophrosyne

    The physics of eye and skin color

    I was reading about why blue eyes look blue. After all, the human body does not create any blue pigment. It turns out, it's the same reason the sky is blue: the Tyndall effect. When there is minimal pigmentation, the first frequencies of light to scatter are the blue frequency waves. When there...
  47. R

    B Understanding Color & Temperature

    In my quest to understanding radiation of the electromagnetic spectrum and the things around me I would like to confirm if I understand this correctly... - The color of objects around us doesn't always mean they are hotter than another just because of the color it has, for example: A blue...
  48. Isolde Wilde

    B Can color be used for measuring density?

    I am wondering if can the colour of a liquid be related to its density?