WHY are the veins blue if the blood is red?
The bluish or greenish tint of veins is due to the way light passes through layers of skin and subcutaneous fat. When looking at our arm or leg, we see the picture of light reflected from the tissues.
Skin is weak in transmitting light, unlike blood. Yet red waves of light penetrate the tissues better than blue. Blood, on the other hand, more readily absorbs blue and purple light, which explains why we see it as red. When a blood vessel runs close to the surface of the skin, almost all of the blue light is absorbed by the blood and some of the red light is reflected
