The Loom: Return of the Howlers discusses color vision and how fruit-eating primates rely on smell, while leaf-eating primates rely on color vision to discern good food from bad. It’s not quite clear why we have such excellent color vision, but it probably contributed to our poor sense of smell (and to our reliance on visual cues, not pheromones, to attract a mate):
We have three genes that make receptors for light in our eyes, each sensitive to its own band of the spectrum — red, green and blue. The combined sensitivity of these genes lets us tell the difference between yellow, organge, pink, and red. Other apes and monkeys in the Old World also have trichromatic vision, as it’s called. On the other hand, almost all monkeys in the New World have only two color genes, as do lemurs, which are the most primitive of living primates. One gene is sensitive to blue, and the other is broadly sensitive to the red-to-green part of the rainbow. As a result, they can’t discern colors as well as we can.
Of course, some humans don’t have trichromatic vision; they have red-green colorblindness. While I realized that many animals were colorblind compared to humans, I didn’t realize that humans were effectively colorblind compared to birds:
As these primates depended more on this visual language of love, their pheromones became less important. Birds support this hypothesis — they have four genes for color, giving them even better vision. And instead of pheromones, they depend on beautiful feathers and combs to attract mates.