If blood is red, why are veins blue?
(Najamuddin Ghanghro, Karachi (original from Larkana))
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.