Blue or green light, on the other hand, doesn’t travel as deeply. They are more easily deflected from your skin than red light. So when white light hits your skin, blue and green light isn’t absorbed in the same way as red light. The result is that, despite blood always being red, you ultimately see blue or green veins. Visible Blue Veins on legs can be a sign of vein disease and should be evaluated by your doctor.

When left untreated, vein disease can place you at increased risk for several dangerous health conditions. These include blood clots, pulmonary embolism, and venous ulcers (open, non-healing wounds). It is important to know that sudden prominent blue veins that appear on your legs can be a sign of trouble.