The Green Stool .Net: Stools that have an unusual color may be due to diarrhea; intestinal bleeding; intestinal, pancreatic, or liver disease; and medications. A common shift of stool color is the green stool or poop. Diarrhea transfers food so rapidly through the intestine so that the intestinal chemicals and bacteria do not break down the bile pigment to the natural brown color, or the green color may be due to some foods such as green, leafy vegetables, or green food coloring. It may be due to bile pigment in the stool.
In the digestive tract (esophagus, stomach, small intestine, or colon), red or black poop can be a sign of bleeding, and should not be overlooked. What tests need to be conducted depends on what cause is assumed for the shift in stool color when stool color changes. For example, if bleeding is suspected, a gastrointestinal tract endoscopy may be needed to assess red or black stools.