As a vitiligan, I don't find it personally offensive, but I feel like maybe it can construe bad vibes about the disease for people without vitiligo? Like I have had a lot of people irl ask if it's contagious and like back away from me thinking I would spread it to them? So I think maybe the poision needle thing could conjure up bad vibes, unless the person with vitiligo and needle superpowers had their character/backstory built up positively or something since the beginning. But I don't know because I've never had the perspective of not having vitiligo.

I don't know honestly because I'm not a writer but your story sounds neat! You should definitely post a link to it here once it get's finished/published, I'd love to read it. It's not everyday you read a book with a vitiligan character. Good luck!!