Listen peoples. It. Is. A. Game. People are allowed to have impossible hair colors/styles, and the Japanese like to exercise this ability often in their games/anime. Silver is his natural hair color. That's it. He didn't dye it, he didn't do any crap to it, it's just silver. End of story.

And everyone's hair is kinda shiny, though more of a dull shine and not sparkly oh-em-gee-it-burns-my-eyes shiny.