Coffee, strong tea, tobacco and some foods can affect the appearance of the tongue's surface. A brown colour may involve a coating, but the cause of a specific change cannot be determined online.
Avoid aggressive scraping
Gentle tongue cleaning and regular dental hygiene are a sensible starting point. If you use a scraper, make a few light passes instead of pressing hard repeatedly.
A change that does not disappear despite good hygiene, worsens quickly, hurts or has an unusual texture should be shown to a professional.
