Green is a very common color in nature. Not only among vegetation (obviously), but also for many creatures such as reptiles, amphibians and insects. However the coloring in question it does not appear to have been gifted to mammals. Why aren’t there any mammals that have green fur or skin?
The latter, in fact, usually have hairs, which have specific and well-defined properties, including pigments. Meanwhile, it should be noted that there are no creatures of this color. The green animal and mammal closest to this conception is the sloth, which has this color because it carries many algae and mushrooms.
The reason is simple to understand: i hairs are not capable of producing green or blue pigments. The same is true in humans: there are lighter pigments, such as blond and orange, and darker ones, such as brown and black. No combination could ever create this color naturally.
Everything is to be found in the evolution: what advantage would a totally green creature have? Many animals have undergone thousands of years of development to become exactly what they need to survive and, like pandas that have this color for a very specific purpose, this is the reason why there are no “Hulk” colored mammals.