I just started taking probiotic capsules. my first bowel movement was very dark brown?

Probiotics are just collections of bowel friendly germ colonies (seeds) that can help balance the type of germs living in your gut. Color of stool is based on the action of various factors on the ultra-green bile added by the liver. The longer debris remains in the digestive system, the more it changes from green to yellow to browns. I don't consider this a problem.