The green color of the stool is usually indicate that our bowels are passing through the intestine faster than normal. The green color is due the bile. As bile makes it way through the intestine it progressively changes its color from green to yellow to brown. When the bowels pass through the intestine faster than normal it does not allow time for these changes to occur and the stools are green in color as a result. Green colored stool can be due to intake of certain foods, diarrhea, food poisoning, laxative use, antibiotics use among other causes.
Usually this is a harmless condition and will go away on its own.