The color of blood vessels varies by vessel type and individual circumstances. In general, the outside of the arterial vessels is wrapped and surrounded by a white connective tissue that appears white from the outside. Leaving aside this connective tissue, the arterial vessels are mostly red or bright red in color due to the oxygenation of the blood in the vessels. The venous vessels, on the other hand, are mostly dark red in color because the venous blood has delivered oxygen to all parts of the body, so when you look at the vessels themselves alone, they show up as mostly dark red in color. However, because the human skin is mostly yellow, and some people are thin, the sebaceous layer is thin, from the outside of the skin to observe up the color of the veins to greenish purple, and even some people will appear blue. As long as the blood vessels do not appear worm-like, lumpy varicose, the color of these vessels belong to the normal range.