Poop is normally brown because of pigments that come from bile, a digestive fluid made by the liver. Bilirubin, a yellow pigment produced when old red blood cells are broken down, is released into bile and eventually reaches the intestines.
Once bilirubin enters the intestines, gut bacteria help change it into other substances called urobilinoids. One of these substances is stercobilin, which is commonly associated with the brown color of stool. This process is a normal part of how the body breaks down and removes bilirubin.
Stool can naturally vary somewhat in shade. However, stool that stays very pale or clay-colored may occur when too little bile reaches the intestines, such as when bile production or bile flow is reduced. Black, tarry or visibly bloody stool also needs separate medical assessment rather than being considered a normal color variation.
If stool repeatedly loses its usual brown color, especially if it becomes pale or clay-colored, medical evaluation is recommended. A primary care doctor or gastroenterologist can determine whether further testing is needed.