First of all, I think Sauron's cat would be a huge cat like beast that's super friendly (exept when you get him up too early). I like how the eyes seem like they are reflecting the lava of Mount Doom. It has this firey glow that probably means "get out of the way or I'll eat you." I also think Sauron's cat would be black, or gray, but I don't think it would get the same affect as this tabby does. I think it would be cool if the background would be basalt with flowing lava on it, but yet again, it wouldn't get the same affect as on the tabby. It's hard to tell that the eyes are edited because it blends in so perfectly, of course beside the fact that that's not a natural eye color for a cat. Over all, I think this is a good piece of art, and it really catches the eye.
Beautiful capture. By the way, this cat must be very old, you can usually tell how old a cat is by looking at the iris. Cats will develop something called "iris atophy", which causes the eye to look weird like this. It is a natural result of aging.