I need to cover my grays, too. I just couldn't use chemicals anymore. I did try Robert Craig, and it seemed gentler, but I didn't stick with it long enough to see if there was any long-term damage because I found that it faded from my gray quite quickly.
I honestly don't know of any solution other than henna or some type of vegetable dye. All I know is that when I stopped the chem coloring, my hair was completely different within a couple of months.