What does it mean when my bf throws up a dark green almost black color vomit?

Bile: Bilious vomitus is that color. If he has frequent episodes of vomiting, inflammation of the stomach lining(gastritis), gall bladder problems, hepatitis, intestinal adhesions, peptic ulcer, hiatal hernia are possibilities and he should be examined by a physician. Have him abstain from alcohol,caffeine,greasy and very spicy foods,nicotine in the meantime