Trichromatic vision, often described inappropriately as 'red', 'green'and 'blue', is derived from three cone classes which contain photopigment with relatively long (L), medium (M) and short (S) wavelength spectral sensitivity.
Jacobs of the University of California, Santa Barbara and his colleagues reported that both male and female howler monkeys--New World primates that eat primarily leaves--have fully trichromatic vision. The monkeys all have a second opsin gene on their X chromosome.