Hello Black colour stool is a matter of concern It can be related to internal bleeding inside the intestine If I were your treating doctor I would gave advised you for few investigations like blood for hemoglobin, CBC Liver function test and stool test for occult blood or an endoscopy if need be. You should take lots of fresh fruits and green leafy vegetables Please let me know if you are taking any medicines or having any kind of liver disease or metabolic disease. Thanks for your question, please feel free to ask for more assistance, I will happily answer you Best wishes