Has anyone used this? I just mainly want to know if it will work to keep my hair black. It's fading into a dark brown now (probably due to the semi-perm color fading out). How long will the henna last? My hair is normally blonde, so the roots are starting to show now, and I don't want to keep redyeing w/ permanent color. It just seems bad for my hair when I'm normally so careful about keeping chemicals out of my home and body!