Thank you for your interesting questions.
You appear to be talking about Leukoplakia, which is a condition with white patches in the mouth and/or tongue.
If it is painful, then it can be thrush or a fungal infection. You can try to scrape it to tell the difference.
It is usually harmless and should go away by itself.
However, some conditions can be related to it, such as heavy smoking, bad fitting teeth, or other medical conditions. If you are worried, you can always visit a general practitioner to check it out.
It's true also that a smooth tongue, or a red beefy tongue can mean some vitamin deficiencies. Otherwise, I'm not aware of any other colours being related to medical conditions.
