A good quote:
Most mammals, including mice, are dichromats, possessing only S and M cone pigments. As a consequence, they can distinguish only a fraction of the wavelengths that can be distinguished by humans. John Mollon at the University of Cambridge has suggested that the evolution of trichromacy could have permitted primates to discriminate between unripe fruit, which is typically green, and ripe red- and orange-colored fruits. Reciprocally, the colors of ripened fruits may have coevolved with primate trichromacy, since animals that could recognize and eat the ripe fruit would have assisted plants by spreading their seeds.
Check out the link to the sidebar for a good illustration of red-green color blindness.