Why are mammals less colorful than other animals?

When, some 200 million years ago, mammals, birds and reptiles began to diverge from their common ancestors, the different ecological niches they occupied would later influence the entire order that was being formed.

Due to their way of life, birds rely heavily on their sight, which is among the best in the animal kingdom, while they use their sense of smell very little, which becomes less and less important as the distance from the ground increases.

The predominance of sight and their ability to see many colors made it advantageous for them to develop extremely showy coats for other members of their species.

Mammals, on the other hand, lived as rodent-like creatures with a nocturnal lifestyle, which was reflected in the senses they used and their vestigial structures.

The sense of smell was very important for mammals of the time, living very close to the ground, while sight was much less developed than that of birds, and they distinguished colors very poorly.