Animals do not need color vision to survive...only a few see in color. The rise of color vision in humans is incidental, and recent. Judgeing from Homer's Illiad and Odyssey, the Greeks of Homers age did not possess very much color vision (about 800BC). Other ancient Greek writers used color terms in the same limited way, so we cannot merely think that Homer was colorblind, and other Greeks were not . The possiblity exists that ancient Greek retinas were not evolutionarily developed enough to perceive the full color spectrum.