Thanks for your replies rickj and pretty lady. My hair is totally gray and I've been using semi-permanent hair colour for years. My hair must take to colorant easily because it doesn't wash out totally in 12 to 24 washings. Last time I returned to gray I had to grow it out. Because I like to keep my hair mid-length it took me almost a year to return to gray. I was just wondering if there was such a thing as a gray hair coloring, to cover up the brown hair coloring, but I think you've answered my question. It is "No"! So I'll have to bite the bullet, let it grow out, and keep cutting it.