I don't have vitiligo, but I know that it's an autoimmune condition and is very likely connected to your other symptoms of being gluten intolerant and hypothyroid (I'm going to bet that you have Hashimoto's, even if you haven't been diagnosed!)
It's possible you also have a casein sensitivity, and some people cross-react to coffee the same way they do to gluten, so there are two possible factors. Another possibility is that you have an antigen (like a virus or bacteria) that is firing up your immune system.
Another possibility is that you're taking an herb or supplement that could be stimulating your already overactive immune system (examples: for some people, echinacea, licorice, medicinal mushrooms, beta glucan and astragalus are a problem and for others, resveratrol, green tea, caffeine, chocolate, pine bark extract, pycnogenol and grape seed extract are a problem.)
Iodine can really cause the immune system to flare, so until you know for sure that you are negative for thyroid antibodies, don't take it! The amount of zinc you were taking is fine- it shouldn't cause problems (or you could take a zinc/copper combo.)
There are ways you can balance your immune system so that it stops attacking your thyroid and melanin cells. You can determine which immune pathway is the culprit and modulate it.
I'm going to recommend that you find a functional endocrinology practitioner to help you put all the puzzle pieces together. It made a huge difference for me (I was already Primal but my Hashimoto's was still giving me symptoms and my immune system was not yet balanced).
Check out the practitioner list at www.thyroid.com and if there's no one in your area, I know that a number of them will work distance with you (I know for sure that Dr. Peterson in MO will).