discoloured ankles

As spring and summer approach and I begin to turn my thoughts to cropped trousers, sandals, bare legs and Easter holidays, an old problem is rearing its head again- the little patch of yellowish skin on each ankle! It looks horrible and when I apply gradual tanning lotion to improve the look of white, purply legs, I end up with two dark patches. I think they're due to wearing boots all winter plus sitting cross-legged. I've tried the usual exfoliation and moisturising but nothing seems to work. Any suggestions?