Act Naturals and Grey Coverage?

I'm considering trying Act Naturals. I've been using the Surya Henna but while it's been great for my hair and scalp and no reaction at all, the color is inconsistent on the greys--total coverage is there but sometimes the color is good other times I've had purple and/or a metallic red. I also got a purply color using the black and a black/dark brown mix from Clariol Loving Care. I'm fearing that I won't ever be able to get a "natural" color on the greys with the PPD-chemical free products (which are my only choices) I'm wondering if Gina or someone else knows how the color holds on grey with Act Naturals. I'm very dark brown (to black) with grey (now I think it's at 50%+). In a few years, I think I'll be able to let the greys go, but at 39/40 it's too sad.. Any more info on Act Naturals would be great.

Thanks!