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I didn't think we had any confirmed examples of human tetrachromats?

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..

I'd imagine any combination of {duplication and mutation on the blue cone gene which isn't on X, mosaicism or Klinefelter syndrome, transposition from X or replication on X with mutation} would work for you. Maybe not Klinefelter because of X-inactivation, I don't know how those two things interact offhand.

I _think_ the key point is, as you said, that the different gene copies need to have different response ranges, or you end up functionally trichromatic even though the pigments are from different places.

Her name is Concetta Antico. This is her website: https://concettaantico.com

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