Mine used to be a yellowish white. It was milk residue that built up. Every day or so now I rub her mouth with a washcloth & it's gone. It only got yellowish when it wasn't wiped off in a while. We did our own newborn photos and I had to do a lot of editing to get her tongue looking normal (she was wide mouth smiling in the pic). Good thing she doesn't mind the cloth in her mouth!
Re: Yellow tongue?