Is your baby really young? Just born. If so their boop is supposed to be yellowish very grany looking like mustard. If he or she has an allergy. It would be from formula and that is very noticible early. My daughter was very allergic to similac, we went to soy(isomil) oh boy she vomited and had rectal bleeding. If your child is older, 1yrs or older have them tested. I did and she is allergic to nuts, eggs and milk. Not fun b/c these ingredients are in evrything