Dark green poop

TrueCrimeNerd • Getting off this shit for a while! Good luck and baby dust to everyone.

Hi! We’ve recently started using frozen milk to feed baby and his poop is dark green. It’s pumped milk but he always has pumped milk so it can’t be a foremilk/hindmilk issue or an allergy. The milk is from a few weeks ago and he had no green poop at that time. Any insights? Pediatrician isn’t worried but didn’t really say why it would be happening.