Stool comes in a variety of colors. All shades of brown and green are considered normal and rarely indicate possible serious condition. Stool color is typically caused by the foods you digest and the amount of bile in your stool. Green stool can also be caused by iron supplements.
Bile is a brilliant yellow-greenish liquid that is produced by your liver and is found throughout the digestive tract. Bile digests and absorbs fats in food. As bile travels through your intestines, it is chemically altered by enzymes, changing the color from green to brown. If the intestinal contents travel at a normal speed, stool is light to dark brown. If the intestinal contents travel too quickly through the intestines (called decreased bowel transit time) for everything to be fully digested, the resulting stool is a green color. If the reverse occurs, and the stool remains in the intestines for an abnormally long time (as with constipation), the color becomes very dark.
Consult your doctor if you’re concerned about your stool color.