Blood can turn a dark greenish-black – like Spock’s – if you take a certain type of migraine medication.
(A team of Canadian surgeons got a shock when the patient they were operating on began shedding dark greenish-black blood, but the unusual colour was due to the migraine medication he was taking. The patient had been taking large doses of Sumatriptan, which seemingly can cause a rare condition called sulfhaemoglobinaemia, where sulphur is incorporated into the oxygen-carrying compound haemoglobin in red blood cells. Actually I think he was really a Vulcan. Live long and prosper.)