What is going on in our Mouth with Blue Tongue Sticker? It looks like this person has eaten a lot of sweets with blueberry flavor, and now his tongue is blue. Do you know why sometimes a candy colors your tongue? It is burning because of the large amount of acid that makes up the coating of the candy. This is also why it is red - the acid is quite irritating. If you continue eating them - your tongue will eventually bleed. So be cautious about these evil candies.