My Husband Has Stage 4 Colon Cancerl Metastastis To Liver.

My husband has stage 4 colon cancerl metastastis to liver. He has started to vomit dark green color substance for the past 2-3 days. His chest and throat is burning cause he vomits so many times a day this dark green, sometimes brown/black substance. What could this be? He is unable to eat solid food so only drinks mild tea or honey water