Is having grayish/black stool normal for a 16 year old?

Diet vs problem. The poo color is a reflection of either diet or what your body added to the stool as a waste product. A gray/black stool could be the pepto-bismol you ingested for belly problems or a worrisome sign of abnormal bleeding in the digestive process. Write down all you remember eating over 4-5 days. If no pepto , take the list & a list of any symptoms & review them wit your dr.