UV is my error above I m told by Kimberly Jameson in an email that the fourth range is in or near the reds if I understand correctly at least that it s not UV I now think almost no tetrachromats conversationally distinguish the fourth range but instead almost all have since babyhood been perceiving colors as trichromats do because they re trained that way using pictures and what grownups persistently say Conversational tetrachromacy being rare is probably supported by the absence of any support from almost any business especially businesses with customers who are almost all women and which depend on color perception for customer satisfaction since most would be happy to expand their sales by 2 by carrying products for tetrachromats and staffing with a tetrachromat and advertising it but they don t so the incidence of conversational tetrachromacy among adults and adolescents is likely extremely rare