Ashwagandha is an herb which WebMD cites as being used to treat a condition called leukoderma, which is another name for vitilgo. Ashwagndha can be used to alleviate a number of different ailments as well, and is known to help boost the immune system, reduce inflammation, and benefit the skin. Typically, Ashwaganda is sold as an herbal tincture in alcohol, such as the example product below by Herb Pharm. Ashwagnda is also sold as a liquid capsule like the one below by Gaia Herbs, and it is also available as a tablet like the ones below by Life Extension. It is also sometimes sold as a powder. Regardless of the form, Ashwagandha is taken orally.
Ginger Root has also been know to have an effect on hypopigmentation. Perhaps you've seen this blog called The use of ginger to treat skin hypopigmentation where the author tells her personal story of how using ginger root juice cured her hypopigmentation. The specific instructions of how to use ginger root are detailed in this post from her blog, but it's basically a topical application.There are also a number of other people who tried ginger for hypopigmentation who commented on the site Medhelp.org. If you haven't come across that page on your own, you may find some of the comments about how the ginger helps to blend their skin tones to be encouraging. Though there are many more comments from people who have hypopigmentation problems and want to know if it works than there are people who have tried it and are reporting back.
More herbs for Vitiligo are mentioned in the Herbcyclopedia. The great thing about this website is that each of the herbs mentioned includes a reference to a medical or pharmacological research article about the herb's effectiveness in diminishing the white patches on skin. Many of the herbal treatments mentioned are part of the Ayurveda tradition.
To learn more about Ayurveda, see this book recommendation for more info: The Way of Ayurvedic Herbs: A Contemporary Introduction and Useful Manual for the World's Oldest Healing SystemThese Ayurvedic herbs may be difficult to find as ready-made tinctures or concoctions. Some involve herbs that are more readily available for sale, such as Ginko Biloba and Guggul Resin. Examples of these herbal remedies are also included below.
Remember, herbal remedies are not regulated by the FDA so concentrations and dosages may vary widely depending on the product. If you go to your local health food store, you'll likely find the people that work there are very knowledgeable and passionate about what they do. And if they don't know the details you need, they have the resources to find out, either through product literature or by contacting their sales reps.
Naturalpathic Treatment of Vitilgo is also available. If you're really interested in exploring natural treatment for vitilgo, then you may even be want to look into seeing a naturopathic doctor near you who could give you more personalized recommendations as well. (You can click on the link to search their database of naturopathic doctors in the US).
To learn more about natural ways of treating vitiligo, the book Wanakee' s Nutritional Approach to Vitiligo & Other Autoimmune Diseases: A Naturopath's Personal Journey Toward Healing Naturally
may be helpful. The author, Wanakee Hill, is a naturalpathic doctor who suffered from vitiligo herself, and she tells her personal story as well as what methods she uses to successfully treat herself and others. 
