Baby poop on FM

Hi mommies, I noticed that my baby poop has been in this very dark green colour for a week. He's 3mth plus now. He's been on mixed FM and BM before this, but on the 3rd mth he's on full FM. His poop colour was the usual yellow mustard and/or dark brown, until recently it changed to dark green. Is this normal or is the milk not suitable for him? #advicepls #firstbaby #1stimemom