I wouldn't worry too much about a day or two of green stools. If you see a pattern of more than a week or two, then you may want to consider seeing a GI doctor.
Probiotics are good/friendly bacteria that helps your body. One of the best sources of probiotics is kefir. Yogurt is also very good.
Here's info re: ibs and probiotics: Irritable bowel syndrome
(IBS) is a functional bowel disorder that can be characterized by symptoms of abdominal pain, cramps, gas, bloating, diarrhea and constipation. Surveys estimate the prevalence rate ranging from 10-20% of the adult population and the condition is diagnosed 3 times more often in women than men (FDA Consumer Magazine, July-Aug, 2001). Only a few controlled studies have been conducted evaluating probiotics and IBS. Some symptom relief (primarily from diarrhea or abdominal pain or bloating) has been reported in studies published to date.
**I attribute probiotics to getting rid of my toenail fungus. Check out some of my other posts regarding the matter**