My son is 8 weeks old and breast fed. He has had white residue on his tongue (not anywhere else in his mouth) for a month or so now and at the last visit the Dr. said it was just milk residue. The past week or so we've noticed that the white coating also now has darker patches on top of it - like blackish/blueish. It kind of scrapes off but it's hard to get my son to open his mouth to let me do so. He has never been on antibiotics. I'm pretty confident that the white patch is just milk residue and not thrush, but the darker patches are worrying me. Is it just lint? Mold? Anyone else have this?