The only time I've seen this (color of stool) with myself, is when taking Iron or more of it.
There are generally two causes for a green bowel movement.
One - something you have ingested, such as large amounts of green, leafy vegetables, green or purple artificial colouring, or any vitamins or supplements, even if they're not green in color, such as iron.
Two - A variation in the gut transit time, particularly fast transit caused by diarrhea and IBS. Bile that is secreted in the first part of the small intestine is actually green. As stool is digested and passed through the large intestine it is turned into a darker brown color. If stool is still green by the time it is excreted, it could mean that it went through the large intestine too fast to be changed in color. This is often called "rapid transit" or "decreased colonic transit time" and diarrhea that is green in color could be the result.
However, if green stool continues, or your bowel habits have changed in other ways, you may want to call your doctor. This is especially true if you are experiencing diarrhea which can be an indication of other problems or could lead to dehydration.
Good Luck!