Answer:
A yellow discoloration to your tongue is called Yellow Tongue. It is usually a harmless problem that is temporary, but can be an early sign of black hairy tongue (also a temporary, harmless condition). Usually, self treatment is all that is needed for Yellow Tongue, but you should see a doctor if the discoloration persists or the whites of your eyes have a yellow discoloration (sign of jaundice), too.
Yellow Tongue can also be an indication that there is a problem with your gallbladder or liver.