If blood is red, why are veins blue?
Blood is bright red in its oxygenated form and a dark red in deoxygenated form. In simpler terms, it is bright red when it leaves the lungs full of oxygen and dark red when it returns to the lungs for a refill. Veins appear blue because light penetrating the skin is absorbed and reflected in high energy wavelengths back to the eye. Higher energy wavelengths are blue.
