What does it mean if my baby has green diarrhea?

Nothing: The color of diarrhea is not important-- unless it's red with blood. Green means the gut is moving quickly, and you're seeing green bile. But that really doesn't mean anything special.

Probably normal: Many infants have frequent bowel movements and parents often consider that to be diarrhea. The color of the bowel movements, while often yellow, can be brown or green. Blood in the stool, mucous in the stool, feeding problems, lack of weight gain are all red flags that should prompt you to contact your pediatrician. In the absence of any concerning issues, green stools are probably normal.

Normal variation: The color of poo is derived from the waste pigment that end up in the bile, which is added to the intestines from the liver. It starts out an intense green & over time may change thru yellow & brown. The germs of the intestine convert the pigment as it transits the digestive tract. The less germ action the less color change. Diarrhea is often a greenish color for this reason.