Canadian surgeons were shocked when the patient they were operating on began shedding dark greenish-black blood. The patient was not Vulcan - the blood was down to the migraine medication he was taking.
The patient had been taking large doses of sumatriptan and this had caused a rare condition called sulfhaemoglobinaemia, where sulphur is incorporated into his haemoglobin. Describing the case in the Lancet, the doctors "The patient recovered uneventfully, and stopped taking sumatriptan after discharge.
In Star Trek, Mr Spock had green blood because the oxygen-carrying agent in Vulcan blood included copper, rather than iron. Copper, rather than iron is a key component of the second most commonly found respiratory pigment in the Animal Kingdom. Haemocyanin is found in Molluscs but gives their blood a bluish tinge when oxygenated.
I'll pass on a picture of Spock or a mollusc for this post...