I use a tongue scraper every day in real life which I'm sure figures in to this. In my dream I see my tongue is perfectly clean but the rest of my mouth is coated in yellow. I'm horrified but convince myself it's from eating turmeric (for the record haven't been eating well, or any turmeric, lately).
It means you are spending time cleaning your tongue, however you aren't paying attention to the rest of your body where the real concerns are. I'd be betting there are other health related dreams that are telling you what they are and how to pre-empt them.