As food moves through the digestive tract, it turns from green to yellow-orange to brown as a result of reaction between bile and enzymes in the bowel.
When the bowel movements are frequent and in form of diarrhea, the food is passing too quickly through the digestive tract and stool may not be absorbing enough bile, or there is not enough time for bile to react with enzymes and change its color to definitive brown.
This will result in diarrhea like stools of orange color.

Best wishes!
Marija