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First of all, the "colors" are just they way our brains draws decision boundaries between light of different wavelengths, they don't actually exist. Now brain does it by looking at the amount each type of cones in our eyes is activated, hence our "rgb programming", it's literally encoded in our biology.
Green is weird, as you can see from the picture, wavelength span where green activations are dominant is actually very short, it almost overlaps with red. I think there was some evolutionary explanation for that, bit I forgot it.
