Patchy and blotchy legs??

Melisa

So, for the last 2 years Ive realised that I start getting patchy legs while standing. As soon as I lift my feet up it goes away. When it gets patchy its like my legs start turning darker and I get like white blotches all down my legs... Last year when I started tanning it was unnoticable but, as soon as I lost my tan its all blotchy again when Im standing for too long. Any idea of what this could be?