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Color is formed by mixing light of different wavelengths, so a color could be represented as a function which gives the amount of light of each wavelength.

My question is, if white light is a mix of all colors (a straight line on this graph), then how come it can also be created by mixing the colors red, green and blue (three spikes on the graph)?

Does mixing two wavelengths somehow combine them into one?

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    $\begingroup$ physics.stackexchange.com/questions/12046/… Premise is different, but pretty much answers the question. $\endgroup$
    – QCD_IS_GOOD
    Commented Jan 1, 2015 at 23:20
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    $\begingroup$ Colors are excitations of three different receptors in the human eye. Unlike spectra they are perceptual information but they aren't "physical" in the sense that a certain wavelength of light is. Because a spectrum contains an infinite number of wavelengths, but the human eye can only perceive three classes of visual perception, there is an infinite number of physical spectra that will lead to the exact same perception. And, yes, this has been asked many times before. $\endgroup$
    – CuriousOne
    Commented Jan 1, 2015 at 23:20

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You can create the same perception of color in different ways - that is, with different mixtures of colors of different wavelengths. Because "color" is something that only exists inside the mind of the observer (as opposed to "wavelength" which is an objective quantity), you really need to understand how color perception works.

I refer you to an earlier answer I wrote: https://physics.stackexchange.com/a/108795/26969

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  • $\begingroup$ @Someome - yes, that could happen. Years ago they made a hard-to-forge 500 guilder bank note in the Netherlands that included a picture that was invisible under daylight but if you looked at it through a color filter, it was quite distinct. You can see it in a youtube clip made of the note - the rabbit at 1:04; or just see this snapshot $\endgroup$
    – Floris
    Commented Jan 1, 2015 at 23:48

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