where does it says that he has vitiligo?
His half white hair is a type of vitiligo iirc
Sakura has piebaldism and heterochromia
Oh this could also be it tho but vitiligo also causes white hair and affects eye color and the fact that they're both located at the same side so I assumed that was the case. Japanese people usually have fair skin color so the discoloration might not be too noticeable.
I'm gonna be really sad if Sakura's parents alienated him because he has vitiligo ☹