Translation:He wants a pink hat.
欲しい is used for things you want ("I want cake") and たい is used after a verb as an auxiliary to express an action you want to do ("I want to eat cake"). I doubt either is particularly polite since, in Japanese, speaking about your own desires isn't really seen as polite in general.
Can someone please correct me if I'm wrong here:
I was at first surprised about the use of the subject-particle が in this sentence, as I considered "かれ" the subject and "ぼうし" the object. I would therefore have imagined that the object-particle を would be used in stead of が. However, someone mentioned that ほしい is an adjective in Japanese, not a verb as in English. So the sentence isn't saying "he wants the hat", but rather "the hat is wanted (by him)". In this way, the hat is the subject, and が is the correct particle.