Ring Lookalike Red Mark On Ankle. Uneven Spread Boarder Changes

Ring lookalike red mark on ankle. Uneven spread boarder changes colour when im cold to red or after a hot shower. I dont know what it is im 22 years old history of using sunbeds. However I had a bad accident when I was younger tore a cartlidge im not sure if I damaged my ankle then as I was so concerned about my knee. Been there for 4 years doctors say pigmentation nothing to worry about it is quite large. When I touxh it turns white then back to colour again ; (