all the fourth cone can really do is give you a higher resolution Higher resolution in distinguishing shades of color. nobody can see infrared or ultraviolet.

all the fourth cone can really do is give you a higher resolution Higher resolution in distinguishing shades of color. nobody can see infrared or ultraviolet. If the fourth cone sensitivity is shifted outside of the currently visible spectrum, then the carrier would be able to see infrared or ultraviolet -- there's nothing in physics or biology that would preclude it.