Colored stool can be caused by a number of different things... bad liver or gallbladder, lots of veggies, bleeding ulcers, supplements, and medications - Pepto Bismol especially.
Here's a list I got off of pediatriceducation.com:
The causes of stool color changes are listed below by body/cell contents, diseases, drugs, foods, infections and other causes.
- Red/Pink Stool
- Blood
- Diazepam syrup
- Ampicillin
- Viprynium
- Phenophthalein
- Red Jell-O
- Dioralyteoral rehydration solution
- Yellow Stool
- Normal in formula-fed babies
- Green/Greenish Gold Stool
- Normally in fully breastfed babies
- Stomach infection
- Black Stool
- Blood
- Iron
- Pepto-Bismol
- Black licorice
- Blueberries
- Green-leafy vegetables
- Lead
- Charcoal
- Coal
- Dirt
- White/Clay Colored Stools
- Malabsorption
- Biliary system blockage
- Barium
- Aluminum Hydroxide