Stool Colour Chart A quick clinical guide to interpret stool color changes and their possible causes. Stool appearance can give important clues about gastrointestinal healthbut always correlate with history, examination, and GASTROINTESTINAL HEMORRHAGE (2): Melena. Melena, the passage of black, tarry stools, usually implies blood loss greater than 500 ml originating anywhere between the oropharynx and the right hemicolon. Melena occurs most often, Black Stool Vs Dark Brown GASTROINTESTINAL HEMORRHAGE (2): Melena. Melena, the passage of black, tarry stools, usually implies blood loss greater than 500 ml originating anywhere between the oropharynx and the right hemicolon. Melena occurs most often,