Source? edit: You may be confusing tetrachromacy with people who don't have a lens and can therefore perceive ultraviolet light that's normally filtered out. T

Source? edit: You may be confusing tetrachromacy with people who don't have a lens and can therefore perceive ultraviolet light that's normally filtered out. These folks can see shades of violet where other people don't because the blue receptors are being stimulated by the ultraviolet light.