I have a problem with the "Star Trek Canon" on Vulcan Blood. Here is the situation:
STAR TREK CANON
Vulcan blood is green colored due to using Copper instead on Iron
The color of blood differs according to the presence or absence of respiratory pigments and the type of pigment used by an organism. Hemoglobin transports oxygen (or carbon dioxide) using iron, thus humans have blood that is colored red. Many deep sea arthropods and some molluscs use hemocyanin which gives their blood a faint bluish color due to the presence of copper. Thus hemocyanin (which Star Trek Script Geniuses deemed the proper protein molecule of the vulcan blood) was actually supposed to be the Andorian blood, because they have BLUE colored blood and they live on a FROZEN world (which matches the Earth deep sea environment of the arthropods and molluscs).
QUESTION FOR THE AUDIENCE
What would actually be (in-universe terms) the metal running in the protein molecule which could taint a Vulcan's blood green? (right now I'm interested in the metal taint only; the reason for it I may be able to come up with (role-play game))