Interesting information from http://www.mayoclinic.com/health/stool-color/AN00772
from Michael F. Picco, M.D.
Stool comes in a range of colors. All shades of brown and even green are considered normal. Only rarely does stool color indicate a potentially serious intestinal condition.
Stool color is generally influenced by what you eat as well as by the amount of bile — a yellow-green fluid that digests fats — in your stool. As bile pigments travel through your gastrointestinal tract, they are chemically altered by enzymes — changing the pigments from green to brown.
Consult your doctor if you’re concerned about your stool color. If your stool is bright red or black — which may indicate the presence of blood — seek prompt medical attention.
|Stool color||What it may mean||Possible dietary causes|
|Green||Food may be moving through the large intestine too quickly, such as due to diarrhea. As a result, bile doesn’t have time to break down completely.||Green leafy vegetables, green food coloring, such as in flavored drink mixes or ice pops, iron supplements.|
|Light-colored, white or clay-colored||A lack of bile in stool. This may indicate a bile duct obstruction.||Certain medications, such as large doses of bismuth subsalicylate (Kaopectate, Pepto-Bismol) and other anti-diarrheal drugs.|
|Yellow, greasy, foul-smelling||Excess fat in the stool, such as due to a malabsorption disorder, for example, celiac disease.||Sometimes the protein gluten, such as in breads and cereals. But see a doctor for evaluation.|
|Black||Bleeding in the upper gastrointestinal tract, such as the stomach.||Iron supplements, bismuth subsalicylate (Kaopectate, Pepto-Bismol), black licorice.|
|Bright red||Bleeding in the lower intestinal tract, such as the large intestine or rectum, often from hemorrhoids.||Red food coloring, beets, cranberries, tomato juice or soup, red gelatin or drink mixes.|