Melena vs hematochezia symptoms and differences Stool Colors and What They Can Tell You Your stool color can carry important clues about digestion, diet, or even disease. Most shades are harmless, but some changes signal the need for Dark stool vs black stool the difference can be serious. Dark brown stool is often food or iron related. Black, tarry stool may indicate internal bleeding and needs urgent medical attention. Decisions: A 20 year old male with dark stool Department of Emergency Medicine Saint John