How to get rid of discoloration around anus?

I have a blue/purple bruise discoloration around my anus, I've had this or noticed it 4 years ago and it hasn't let up. It looks like it's a bruise but there's nothing there, no physical damage, no tearing, no scarring, no wounds, no hemorrhoids, no nothing, not even painful at all. Just pure discoloration, how do I get rid of it? I hate it, I'm very self conscious about this