Thanks Dennis.
I was actually wanting to change the icon color due to contrast. And when I said that I liked the black background, I was referring to the edit area. But, yeah, black\dark in the Line Prefix area works (now I know that it is called Line Prefix). I am still not crazy about the icon color, but the main issue for me was the contrast. I really couldn't see it well (mild color-blindness I guess). So this solves it and I like the black\dark Line Prefix area.