I've also heard green stools can be a sign of a stomach ache (I could be wrong though). Also if you are taking vitamins that have a green outer coating this can also cause green stools. I would call the doctor if this keeps up any longer because you could very well become dehydrated quickly.
Usually when the bowel movement is green it means that it hasn't been inside for very long, meaning that it's been through your bowels quickly. You should try to remember what you ate because that can help you know what gave you the runs, if it continues you should seek medical help.