green is because of the presence of iron as an oxygen carrying pigment. (And to quickly debunk another popular blue-blood myth: No- deoxygenated human blood does not turn blue. It turns dark red. On
Finally, violet blood is also possible, as is seen in some marine worms. These worms have in their blood yet another different respiratory pigment, called haemorythrin. Haemorythrin contains individual units which themselves contain iron atoms; when deoxygenated, the blood is colourless, but when...