Taking 1/2 ounce of liquid chlorophyll extract 3 times a day will make the gray go away, it also can make hair grow back thicker. This takes about 3 weeks to notice but it works. in some cases it can reverse baldness.
Make sure you get a very strong chlorophyll extract, and that its liquid and take it consistently. Shake it up well before dispensing. They have a mint flavoured one which isnt too bad, it stains so careful when pouring it.
I stumbled on this while reading a Gary Null book, began taking it and was surprised by the results.
Another supplement I know will reverse gray hair is resveratrol, would have to take a dose of 100 mg 2 times daily or higher to have this effect.