Tidus with black hair would have severely pissed me off. It would have given him a physical "edge" he doesn't have. Blonde hair suits him better, both in the sense of his overall appearence and his mood and antics as a character.

I am somewhat confused as to why they decided to change his running animation, however. It looks much smoother there when compared to the bopping motion that seemed to plague Tidus in the release version. Oh well, a minor detail really...