Translation:He wears a blue sweater.
7 months later and has "jumper" been added as an accepted answer for ANY of these sentences? It still hasn't for this sentence.
I've been reporting all these sentences continuously since much farther back than seven months ago. Luke has done a fantastic job at sorting out thousands of accepted answers since recently joining the contributor team. But, as far as I know, there's still not yet even a single instance where they've allowed "jumper". I often wonder if it could be that none of the contributors understand "jumper". Here in England, I don't think I've ever called a jumper a "sweater" in my life. ^^;
If there is just one sweater, you would say "He is wearing a blue sweater" or "He is wearing the blue sweater" (notice the use of "a" and "the").
Also, in your post here, I think you should use the word "correct" instead of the word "true." I believe "true" sounds like there really is someone wearing a blue sweater, but "correct" sounds like the sentence is the right answer to the question.