Oddly enough, I was at a FS campground near Durango, Co. (of all places), where dumping gray was allowed. I did, but it felt odd.
In all our years of camping, I cheated once. This past summer, we were in Wyoming, hours from anything. I had 400 pounds of gray with me from the night before, and 500 miles to go that day. I decided I could live with myself and that it might put a few flowers on the dyeing shrubbery nearby. I wouldn't do the same anywhere near people or on a site that the next guy might not appreciate it.