Originally Posted by bjlockie
That does nothing as my user or root.
I am using KDE.
You shouldn't be runnings commands you don't know as root. :-)
Anyway it seems that KDE opens an XWindow on top of X root window, as that's why it appears that xsetroot isn't doing anything. I suppose you can use KDE's control centre to change your wallpaper to certain colour then. Just try difference colours and see if you can find any bad pixels on the screen.
If you can't hide KDE's widgets to get fullscreen, I guess you could try to configure one of the screensaver to show blank screen with certain background colour, or try to create HTML pages with certain background colours and run a browser in fullscreen. Or create a movie with each frame with one colour only. Or...