Not sure what the exact cause is.Never heard any complaints from parents about dark stools following neocate
. Some more information will be useful.For example, how are the growth and developmental parameters .Did the baby get vitamin K soon after birth ? Best to get the stool seen by a doctor or get stool examination done to confirm if there is blood and also worth doing a culture(If growth is not adequate).
I would be very cautious before ruling this out as normal.