How many colors are there?

Is there a finite number of colors, or infinite as I suspect?

Infinite, as you suspect.

I think it is infinite since you only have to adjust wavelength to get a different color and there should be an infinite number of incremental steps you can do that in.

Then again quantum physics has shown the quantized nature of things so perhaps wavelength is quantized as well (i.e. wavelength can only change in discreet steps and not be infinitely variable). I do not know if that is the case but if ti is the number of colors would be finite albeit quite high.

FWIW most computers/monitors today handle about 16.7 million colors so the ‘real’ number is bound to be somewhat higher than that if the answer is not infinite.

Bordelond, and how did you come to that conclusion? Please show your work.

This has come up a few times, someone might want to look up the other threads, in short the wavelength of light is continous but the abilty of humans to distinguish different colours is limited.

Waitaminnit… Since energy is quantized, doesn’t this mean that there is a positive number (oh, Gawd, epsilon!) such that two wavelengths of light differing by that (in nanometers, perhaps) cannot be distinguished.

Finite, sez I.


btw the ‘colours’ of wavelengths out of the visible range actually cycle through the different colours of the visible range (at least it does when you construct a mathematical model of how colours mix together).

No, only the energy of light of a ceratin frequency is quantized, e.g. a light wave of frequency f can only have energies that are mutiples of hf where h is Planck’s constant.

Well, “color” isn’t really a frequency, but rather a perception, based on receptors connected to the brain. In humans there are three types of receptors, so “color” (for humans at least) isn’t a one-dimensional quality, but rather a point in a 3-dimensional space. For example, there is no “white” frequency, or “pink” or “grey” frequency.

Oh, and if you throw in color perception by other animals, it increases the number of colors enormously, as some of them have (I think) 6 or 7 different types of receptors.

Which doesn’t answer your question, I know. My only point is that discussing frequencys is a bit tangential. (although not completely irrelevant).

My assumption is that the answer is “finite, but very large.”

Hmmmm. After thinking a bit further, and building on the idea that “color” is by definition rates of perception in three types of receptors in humans, perhaps the answer is simply three: blue-green, green-blue, and greenblue+red. Every color known can be built out of a combination of these. Of course, I’m counting “blue-green” as one, when truly it’s a sliding scale from black to full bluegreen, but I think the argument could still be made.

Of course I should openly confess that my knowledge about the physiology of sight is highly limited at best.

I’m curious about this too, and I’ve sometimes wondered how many colors are in a beautiful sunset.

I realize that some people are better able to distinguish between two different but similar wavelengths, and I’m guessing that some people can see further into the violet and red ends of the spectrum.

It might be fun to spekalate then how many wavelengths are possible to see between the two ends of the visible spectrum. Anyone have those numbers handy?


I don’t see how the possible number of wavelenghts can be truly infinite. we have boundaries on either end.

On the small end I don’t think you can get a wavelength smaller than the Planck length 1.6 x 10[sup]-35[/sup] m and on the large end you can’t get a wavelength larger than the universe (~ 15 x 10[sup]9[/sup] light years…give or take a few billion).

I also don’t think you can tune, even theoretically, an infinite number of times between any two given points (ala Xeno’s Paradox). Again I think you would at the minimum be limited to Planck Length adjustments.

Granted, given the assumptions above, the number of possible ‘colors’ (wavelengths) is staggeringly large but it is not infinite. Am I missing something?

So much science - and I’m just a color-blind guy wondering what I’m missing…

My guess would have been infinite - but human perception being the limiting factor producing a finite range of incremental differences.

Of possible interest is that I recently met a optometrist who invented contact lenses for color blind people to allow them to see colors normally. Their expense puts them out of reach of most people but she’s added me to her clinical trial list so if I get called to participate in a study I get the lenses for free. That should be neat.

Hm? The energy is related to the frequency…and the frequency is the “color.” If the energy is quantized, isn’t the frequency quantized?

Is it always possible for a photon to exist that has a frequency between the frequencies of any other two photons? I thought not, but I’ll be the first to admit that I may be wrong…

(I spend darn near as much time unlearning as learning!)


The human eye is definitely limited in the colors it can perceive. I do not know the actual number but I do know that the 16.8 million colors a modern video card and display can put out is more than the human eye can distinguish (e.g. color # 15,632 and color # 15,633 are indistinguishable from one another to a human eye).

The human eye also works differently from the additive color mixing (red, green and blue) we are taught in school. The human eye uses subtractive color mixing instead which (IIRC) has some notable imlplications but for the life of me I can’t remember what they are. Of course, a lot more goes into vision than just the three primary colors (contrast, luminosity, etc.).

With color blindness I assume you are ‘missing’ (or have faulty) color receptors for one of the primary color (red, green or blue). How contact lenses will fix this I can’t imagine but if your eye doctors say they have something that might do the trick I’m not going to second guess them. If you do get in on the study I’d be fascinated to hear how well they work for you and how they actually work (I assume you’ll be told that). Be sure to report back if you get to try them. (And good luck getting in on the study!)

I have red/green which is fairly common in men (I think 1 in 20). I asked the optometrist to explain how they worked but she was pretty vague. Somehow they manipulate wavelength so a person with too few rods (or are they cones?) can make distinctions. I also know that the lenses don’t work as glasses because they are too far away from the eye itself. The lenses aren’t really intended for red/green deficiency anyway because of the cost - and the hassle. They are really intended for people for whom color blindness is debilitating (they see everything yellow, for example).

While this is true, it should be noted that a computer monitor or TV isn’t able to cover the entire range of colors (referred to as ‘gamut’) perceptible by the eye.

A simple way to see this is to use the CIE chromaticity diagram. (See here for a brief explanation of how the chart works.)

This diagram shows how an RGB source only maps to a triangle on the chromaticity chart. This means that the colors at the edge of the curve can’t be reproduced.

First pure spectral colours - that is the ones defined by a single wavelength from ~430 to 650 nm, like from a prism.
The human eye can distinguish a difference of about 1nm to 6nm depending on the frequency. This gives us about 150 spectral colours that can be distinguished.

When you start mucking around with intensity and saturation this can be increased to discriminating between millions of different colours, depending on the person.

By the way, we should only talk here about percieved colours because not perceived colours aint colours.

No, a photon may have any frequency which governs it’s energy(you can argue about Planck lengths and wavelengths, but you then find yourself with the problem that the wavelength varies in different reference frames)