"I have a brown belt."
Translation:Jag har ett brunt skärp.
It isn't "bruna" because the "a" ending for colors means it is a plural. For example, brun means brown (singular) while bruna means brown (plural). In context: The cat is brown - Katten är brun The cats are brown - Katterna är bruna The reason why it is "brunt" instead of "brun" is because the word skärp is an ett word. The "t" suffix (brun -> brunt) is used on ett words. Unfortunately, you kind of just have to remember which words are en vs ett.