All shades of brown and even green are considered normal. If your stool is bright red or black — which may indicate the presence of blood — seek prompt. Yellowish, greasy, smelly stool - can indicate an infection in the small intestine. It could also be a sign of excess fat in the stool due to a. The color changes can vary from yellow, green, black, clay-colored, bright red, or maroon. Other stool changes include greasy and foul smelling.