I’m not trying to troll, I’m genuinely curious. Thinking about deer specifically, it doesn’t seem like visual camouflage would really help much when hunting them. Deer sense predators by sensitive hearing (big ears) and smell (long snout). Their eyes are on the sides of their head, so they detect motion rather than high-resolution.
So trying to blend in with the surroundings doesn’t seem to be an advantage in this case. Assuming all this, what’s the point of clothing with camo print on it?
Also, green isn’t a colour found in fur. So there really isn’t a way there can be a green mammal. Only two types of melanin exist in mammals, so we’re stuck with shares of white, brown and light-brown-but-we-call-it-orange.
Birds get to cheat with crafty structural colours, but that doesn’t work for fur. So alas, no green, blue, red or iridescence in mammals.
It may not work with fur, but it can work with skin. I submit: mandrills and velvet monkeys!