Some women have the physical advantage of having four types of colour receptor – two of which peak in a different parts of what we would probably call blue. Colour sensors are coded-for on the X chromosome, and these are the phenotypes of 2 alleles at the same locus, so no chromosomally XY man can have both until some further mutation occurs. That’s why men are more often colour blind.

An interesting consequence of this is that any mental-colour-perception gene is more likely to benefit a woman than a man, because women are physically more likely to be able to distinguish colours than men. So, it would behoove it to collaborate well with other genes which are favourable for women (for other reasons) and it’s quite reasonable to expect it to become partially if not totally sex-linked.