What exactly is a Color Glaze and how does it vary from regular hair color? I was reading a box of this at Big Lots and I gather it is not as strong as regular color, like a color booster, but can it be done on hair that has not been colored? My hair has been hennaed? I do have some gray, not much, just a few here and there. My hair is pretty porous 3c/4a. Thanks.