That's actually not true. For instance red and blue are at opposite ends of the spectrum, so you don't get red + blue without green anywhere. That color is pink, and if you look you will see that it does not appear.
A customer's newspaper had spot red but they often used pink in their design and therefore three plates were output instead of two - useless. "Don't use pink, we haven't got pink. What you think is pink is 50% red, use that instead." The other 50% being white.
One cannot expect the naked eye (especially from a distance and through an imperfect picture) to see or not see specific colors or even all of the colors hidden in a rainbow.
I found this:
(PhD physicist responds) The eye perceives six colors in the rainbow. Red, orange, yellow, green, blue and violet. (some people include the violet color of Indigo as a separate color.) But there are also colors in the infrared and ultraviolet present as well. The rainbow is caused by diffuse refraction of sunlight in water droplets. The source of the light is the sun's photosphere. While each atom in the photosphere may emit light at one quantum frequency, the sun is so hot that doppler shifting of the light causes the lines to "fuzz out" so that you see essentially a continuous spectrum of light. The strictly correct answer, would then be, "an infinite number".
But there are also colors in the infrared and ultraviolet present as well.
Isn't this a contradiction? Colo[u]r being those frequencies of light visible to humans... and infra-red and ultra-violet not being among those...?
While each atom in the photosphere may emit light at one quantum frequency, the sun is so hot that doppler shifting of the light causes the lines to "fuzz out" so that you see essentially a continuous spectrum of light.
I might be wrong about this, but isn't the vast majority of the sun's radiation thermal, i.e. blackbody, i.e. continuous in the frequency domain? Yes, there are spectral lines caused by atomic de-excitation, and they are broadened by Doppler shifting due to the temperature of the gas in the sun (amongst other things) but this isn't what the majority of radiation emitted from the sun is.. is it?
Someone help me out here!
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-- Groucho Marx