Varying shades of brown is accepted as the normal stool color but sometimes it may be other colors. Most of these other hues are considered as abnormal. One of these abnormal colors ia green tinge to overtly green color of the bowel movement. It has to be investigated as this can be a sign of various diseases. The condition is even more serious if there is diarrhea that is green.
Source:Green Bowel Movement and Green Diarrhea – What Are the Causes?