If I recall correctly there has only been one human actually shown to have tetrachomacy, and the supposition that there are a exceedingly small number of additional ones. I think there was a mechanism proposed that would mean they were all biologically female, but can't remember details.

It certainly seems to be rare enough to have no practical impact (except to perhaps the tetrachromat, who presumably has different metatmers perception etc.)

> those people are also overwhelmingly women.

As far as I understand it takes having two X chromosomes with different versions of the gene that encodes the receptors for green, so only women can be tetrachromats.