My baby has a greenish brown tongue. I have taken him to be checked and the doctor said it was Thrush, gave me a antifungal medicine to treat it with but it never cleared up. I took him back and they put him on another medicine and still nothing. They have ran blood work and everything checks out fine. He is on a special formula, Pure Amino, I thought maybe it could have something to do with it? The doctor hasn't mentioned it but it did cross my mind.