I don't think the Iodine itself can cause Vitiligo. I have had some small Vitiligo spots on my legs for years, I think they showed up when they started taking Iodine out of the food supply and adding Bromine! Maybe there's a Bromine connection? I've had them for so long I just don't worry about them anymore.
Are you doing the Salt Water loading to get the bad Halogens out? I do at least a teaspoon of Salt a day (not all at once) in Water with Vitamin C powder added. This will help wash out the Bromide and other bad Halogens.