4month old baby boy. breast fed & 2 times formula in a day. dark green smelly poop?

Normal variation: The main agent adding color to the poo is the material made by the liver called bile. It starts out a dark green and goes thru the yellows to brown depending on the influences of various factors in the intestines. Rapid transit thru the system, as may occur with diarrhea or breast feeding may have a green, yellow or brown appearance. Poo smells because of germ digestion of left over nutrients.

Baby poop: can be many different colors naturally and this is not usually a sign of any problem. In breastfed babies anything that the mother consumes can affect the baby's poop. As long as your baby otherwise appears well, and is well hydrated, this is not usually a reason for concern. Signs of dehydration in a baby as illustrated, are reason for medical attention.