Blood in the stool is probably something you should have looked into. Green is usually fine, but I think the colors for concern are red and black (both of which could indicate bleeding).
In summary, stools in breastfeeding babies are predictably green, brown, yellow or orange. It is runny and has curds almost every time. It changes color with viruses, may have a small amount of blood (call your doc) and may come once a day and even taper off to once a week or more after a few weeks of age |