Blotchy leg?

I have had a blotchy left shin for years and I'm not sure what it is exactly. It is most prominent when it's cold out and if I rub it, it goes away temporarily. It's not on my right shin either. When I'm just out of the hot tub or shower it does the same thing, temporarily disappears but reappears shortly afterwards. I'm not very worried about this because there is no pain or discomfort at all, it's mainly a cosmetic issue.