When you look through your skin in your wrist and see your blood veins, do they look blue or red? Most of you will probably answer blue.
The fact that they look blue through the skin has led to many silly conclusions including the idea that blood is blue until it comes in contact with the air. Despite this common misconception, blood is and always will be red. It gets its red color from hemoglobin and interactions between iron and oxygen in the blood.
To get to point of why blood veins look blue through the skin, this is actually an optical illusion created by the skin. Our skin absorbs red light quite well, while blue light is reflected and scattered. As a result, our eyes see the blue light being reflected back at them.
Our skin also produces reddish shadows, which creates a contrasting color illusion that amplifies the blue effect of the veins through our skin.
Blood color varies between different animal species, but no matter what human starts to bleed, we're programmed to have red blood from birth, no matter what our veins look like through our skin.