Green colered stool may be a normal variant as found in a diet riched with green vegetables, spinach, iron etc. Again if the gastric transit time is short bile degradation can not take place completely. As bile is green in colour the stool may turn into green. You have not described whether there is a diarrhoea loke symptoms present or not or any kind of loss of apetite. There may a problem in the digestive system. Take digestive enzyme along with carminative two tsf twice daily after meal. It will decrease gas formation and abdominal cramps. Please decrease fat containing foods in your meal which will decrease bile secretion. Its not a serious problem to concern as the color of stool will become normal as you minimize the fat intake. In refractory cases you may need a stool examination.