others have already given some great advice about food coloring and such. i remember the very first time i had a poop scare i was a kid and i freaked out cuz my stool was green. it was from eating BOO-BERRIES cereal. anyone remember those? any purple dye gives me green stool. also just for future reference. black stool isnt always blood in the stool. I am aware that black tarry stools are a sign of bleeding farther up in the digestive tract but once i had black stools and since my grandfather had colon "C" It freaked me out turns out it was from taking pepto bismol the day before.