Answer:
it must be a rare disease. I've been a doctor for years and haven't heard of this disgusting sign before. you might wanna go check out your gross jugs.
-Dr. Phinley
There's no way that answer came from a doctor.
The reason the veins become visible (they're always blue, they're carrying blood back to the heart and its oxygen that makes blood red) if they weren't before, is an increase in blood supply. This happens during pregnancy but obviously can be caused by other things. Hope that answers your question -iperu