I do not have an explanation, but can think of two avenues to ask about. First, sometimes an elevated bilirubin level (especially a direct or conjugated bilirubin) can give a green color to the plasma. Often an indirect or unconjugated elevation in bilirubin looks dark yellow. An elevation in direct bilirubin is sometimes associated with liver problems.
A second thing to think about is porphyria. This causes the blood to look black green. This is an illness that can cause abdominal pain periodically and can cause a peripheral neuropathy. there are specific tests for this (of urine or stool usually) to look for the various kinds of porphyria. This is a metabolic disease that can occur in association with certain drugs or illnesses or there can be spontaneous “attacks”.
WithHope for cure of these diseases