I am having runny diarrhea and the color is dark green, also I ate a blueberry muffin today can that be the cause of it?

Possibly. If the muffin was bad or contaminated, it could be. However, it depends on what else you ate and if anyone else who ate the same things also got sick. Usually these infections resolve within 1-2 days. If not, see your doctor for an exam and possible stool test.