Tetrachromats include Zebrafish (Danio rerio) and Zebra finch (Taeniopygia guttata, formerly known as Poephila guttata), both having cone cells sensitive to red, green, and the entire ultraviolet wavelength. According to one of several articles on Wikipedia, "A typical bird eye will respond to wavelengths from about 300 to 750 nm (or 400-1000 THz). Tetrahertz waves.
Apparently, it all boils down to the birds and bees and pollination, which as all of us foragers know leads to competition, coevolution, and directional selection. For purposes of modesty, I will not even go there with the mutualism of biological interactions between organisms of different species. Some of the information is too graphically and sexually explicit, fine for Wikipedia but I don't want to offend the more conservative readers here.
Studies for the possibility of human tetrachromats have wide-ranging results, from 2-3 per cent of the world's women who might have that fourth cone to as many as 50 per cent of women and 8 per cent of men. The use of the words and phrases: suggested, could be, thereby possibly, suggested, suggests, may have, and it is not known are not scientific enough for me.
Promising news though, the majority of female new-world monkeys have trichomatic vision and mice can be genetically altered from two cones to three cones, however there is some complex dispute among researchers as to the accuracy (and I might add, relevance).
While internet sources are attempting to explain tetrachromats, human females as well as our fellow primates, are thrown under the genetic bus, blaming females as carriers of major anomalies that cause protanomaly or deuteranomaly, forms of "color blindness" usually found in males.
On a personal note, this explains a lot about my father and husband, who both denied being color blind, yet their clothing choices gave them away. On an even more personal note, I am now convinced that most people, especially on Wikipedia consistently "make shit up", to quote a reliable unnamed source.