I Have This Large Bruise Like Spot On My Lower

I have this large bruise like spot on my lower spine but it doesn't hurt. I've had it for years and I never really paid much attention to it until people started to point it out. It's quite embarrassing and I'm not necessarily sure what it is. I have been told that I have mild scoliosis. Not sure if that helps any. My question is what is it? What caused it? Can it ever go away?