It is not true that blood is blue until it hits oxygen.
Human blood is actually never blue in color although it appears that way through your skin under certain lighting conditions.
The bluish color of the blood veins is an optical illusion as blue light does not penetrate as far into the tissue as red light does.
The science of light is why it appears that our blood is blue.
The colors we see are the result of which wavelengths of light are reflected back to our eyes.
Our veins appear blue because blue light is reflected back to our eyes.
Blue light does not penetrate human tissue as deeply as red light does.
The colors of arterial and venous blood are different.
Oxygenated (arterial) blood is bright red, while dexoygenated (venous) blood is dark reddish-purple.
Most of the time, nearly all red blood cells in the arteries carry a full supply of oxygen.
These blood cells are bright red and the skin is pinkish or red.
Blood that has lost its oxygen is dark bluish-red but never a true blue color.
People whose blood is low in oxygen tend to have a bluish color to their skin.