Thanks for writing in.
I read your query,i thinks there could be following causes of white/yellow tongue-
1.problem with liver/gall bladder
,although it is rare.
So i will suggest you visit your physician and the complete examination done and take a proper treatment according to the cause.
You can follow few things-
1. Take plenty of water.
2.Quit smoking,if you hae.
3.Maintain good oral hygiene
4.Take crunchy foods like-popcorn,broccoli and apples,etc....
Nothing to get worried.
Dr. Gunjan Gupta