Camouflage. Both prey and predator species use it in nature for their own purposes.
Prey species use it to hide or blend in. Whether they match with the foliage or the rest of the herd, it's a survival technique. You can't get picked off if you don't get picked out. Never stand out, that's the name of the game.
Predator species use it to hunt. They meld in shadows and landscapes, either by coloration or clever disguise. The deception is revealed only when it is too late for the quarry. Lure them in and then strike when they least expect it.