--there could be a vascular component to it; are there any positional differences in the onset or severity of symptoms?

Neuropathy of the small autonomic fibers can cause trophic changes along these lines; people with small fiber neuropathy often have autonomic symptoms that can include disturbances in blood flow, blood pressure, sweat response, and the like.

Also, a number of the vascular/connective tissue autoimmune conditions associated with anti-nuclear antibodies can produce such discolorations, and they also often produce neuropathy:

http://neuromuscular.wustl.edu/antib...html#vascassoc

I would think you'd need a more thorough work-up at a major center or teaching hospital