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In case of light, if all colours of light in the VIBGYOR spectrum are combined, we get white light. And if no light is mixed, that's black. But in case of water colours, if we mix all colours (violet, Blue, Green, Yellow, Orange, Red and some more, obviously not every one in the spectrum), we don't get anything near a white colour. Instead, we get a rough blackish mixture.

So, in a way, in case of water colours, we start with white(say if we start everything by mixing stuff into white paint), and then if we mix everything, we get black.

But in light, we start with black(no light), and if we mix everything, we get white.

Assuming the colours don't react, what's happening?

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you are describing the difference between additive colors and subtractive colors. Additive colors are produced by mixing light of different wavelengths together; the sum of all wavelengths is perceived as white light. Subtractive colors are produced by taking away certain wavelengths from white light; the product of subtracting all wavelengths from white light is black.

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  • $\begingroup$ But, you can't get black by blending non-black pigments. The problem is, pigments are opaque, and they don't mix "subtractively." An object painted red looks red because the pigment particles reflect long wavelengths, and an object painted blue looks blue because the pigment reflects short wavelengths. But if you paint an object with a blend of red and blue pigment particles, then some of the the particles will reflect back "red" light rays, and some of them will reflect back "blue" light rays. $\endgroup$
    – Solomon Slow
    Commented Jun 11, 2021 at 17:49
  • $\begingroup$ yes you can get black by blending non-black pigments. in the printing field, this is called process black and it never is as black as a black pigment. BTW it helps to think of colored pigments as bandpass filters in this context. $\endgroup$
    – niels nielsen
    Commented Jun 11, 2021 at 19:07
  • $\begingroup$ Process color doesn't use pigment-based inks. It uses dye-based inks. That's a whole different story because dyes are transparent, and so they do mix "subtractively." $\endgroup$
    – Solomon Slow
    Commented Jun 12, 2021 at 23:22
  • $\begingroup$ Solomon, in the inkjet printing field, getting black by mixing cyan, magenta and yellow ink in the paper is referred to as process black. True black is gotten with a separate printhead containing black pigmented ink. $\endgroup$
    – niels nielsen
    Commented Jun 13, 2021 at 0:49
  • $\begingroup$ Um, OK, Sure, but I don't understand how that refutes anything I said about mixing color pigments. Get a cheap box of watercolor paints and try it yourself. I bet you can't get anything close to black by mixing only the brightly colored paints. $\endgroup$
    – Solomon Slow
    Commented Jun 13, 2021 at 2:29

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