Best I’ve got is sloths. And they’re only green because algae grows on them. And I know it sounds like cheating because they aren’t intrinsically green but before you completely discount it there are animals that wouldn’t be the color they are in a different environment. For instance, flamingos are only pink because of the seafood they eat. If fed a different diet they can be almost white.
I like some of the other suggestions better than this but if you’ve already tried communicating about it and other things haven’t worked, I wonder if for some cases you could convince him to take a video or a picture. Like, if it’s a cool thing he wants you to see instead of interrupting you record it and share it when you’re available instead of right now, interrupting you. Again, I think the other proposals are better but I wonder… if you’re right about the motivation at least sometimes being just wanting to share something it might be worth attempting.
This is an interesting question but I don’t think it is restricted to green. Isn’t the same true of purple, blue and red? I’m not talking about just reddish like human hair or a red panda but truly bright red like a cardinal. I would imagine it has something to do with our evolutionary history. Complete speculation here but laced with a few facts I picked up. I hear the common ancestor of mammals emerged around the time the dinosaurs became extinct and was basically a tiny rodent like a shrew. I wonder if as a small animal that can’t fly or swim it had to hide a lot and basically just came in shades of brown. So maybe any genes for other colors were lost before that common mammalian ancestor emerged and although mammals have lots of patterns they don’t have many colors.