Can't say for sure that I have noticed anything in that area yet, but certainly something to watch out for. I hadn't dyed my hair in a long time, due to the hair loss and fear of chemicals, so I did have some grey showing through. I actually found that when I was taking higher doses of Iodine that it helped with the greys.
About 4 weeks ago I caved in and used a semi-permanent colour (wanted to look for my new job). I thought the other day that it must be getting time to redo it soon, as they wash out pretty quickly, however I haven't really noticed the greys sticking out too much yet.
Will have to keep an eye on it. Wouldn't it be wonderful if inverting really did help in this area.