Why do we see/need colors, why not black and white?

Several researchers have proposed hypotheses about the nature of this selective pressure. Andrew Smith of the University of Stirling in Scotland believes that trichromacy provides an important advantage for fruit eating species. It can be a valuable aid in determining when fruit is ripe. It also makes it easier to find orange-red fruit against a background of green forest foliage. Dichromatic monkeys are like colorblind humans in that they have difficulty distinguishing visually between green and ripe fruit. While this hypothesis sounds plausible, it may not provide a complete answer because many trichromatic monkeys and the apes predominantly eat leaves. Once again, color may be a valuable clue for such species since the edibility of leaves from the same tree or shrub often varies with their maturity, which can be signaled by color. Peter Lucas of the University of Hong Kong observed that macaques use this as a clue in finding the most desirable leaves to eat. Whether the food is fruit or leaves, the ability to see reds would make it easier to pick out a food target in a green vegetation background.