Red patch on cat's tail??

My tuxedo cat, Crowley, has a random copper-red patch of fur on his tail out of nowhere! He didn't get into any bleach or any chemical that could cause this, and it wasn't there a week ago. I've been searching Google like crazy since I found the spot yesterday, and can't find anything similar... Does anyone have any idea what causes this??

Sometimes if cats lick one spot too much the fur will turn a rusty sort of color like that. Maybe he had something stuck on his tail and it took a lot of cleaning to get it off? Or perhaps a bug bite that was itchy he had to chew on.