This Wikipedia article has something about it: https://en.wikipedia.org/wiki/Tetrachromacy Women can, in principle, develop something approaching tetrachromacy because the genes for two cone cell pigments are located on the X chromosone, and women have two of those. If the two copies of the genes are both active, and behave a bit differently, then it's conceivable that you could get some cones that react to a slightly different frequency. The article says some men could also develop this - not sure how, though. On the other hand the article also mentions just a single really verified case of a woman who had true tetrachromacy. After 20 years of study..