User blog comment:Winnetito/Duvet Cover and Pillowcase set./@comment-30307603-20170721132412/@comment-9300845-20170721214150

Yes, it's a legitimate and officially licensed product like Winnetito said. Although I still don't understand Gumball wearing a jacket and a pair of sneakers instead of his usual sweater on those products.

Maybe it's meant to be some sort of anti-counterfeiting measure to distinguish official products from bootleg ones? In the early 90's, most of the Simpsons merchandise featured Bart Simpson wearing a blue shirt, in contrast with his in-show orange one. That way, if you were to find a product with blue-shirted Bart, it's genuine. If you found a product with orange-shirted Bart, it's a fake.