Quote Originally Posted by Slade
It is possible that his hair naturally bleached. When you spend alot of time in the sun your hair bleaches. I know from experience (although, it wasn't as extreme as Tidus, just the tips of my dark hair went blonde). Tidus would spend alot of time outside training and such for his Blitz tournaments and thus, his hair would bleach over time. The only thing that suggests otherwise here is that Zanarkand seems to be always dark.........
This si a possiblity. Since Tidus spends a lot of his time in those blitzball sphere things the water enhances the suns rays and bleaches his hair.