I post this for archival purposes and the greater good of all mankind since I had little luck in finding a solution on Google quick enough.
Some things make me mad. Enough to want to start pulling my flesh out in clumps. This includes controlling all things in my environment down to even the smallest detail. So when I lose the ability to change my desktop background I seriously lose sight of all reason until the pain goes away.
I was at work connected to my Linux workstation, using Gnome’s Remote Desktop setting aka VNC aka VinoServer, through a ssh tunnel when lo and behold the power flickered at home and shut the workstation down. When I got back home I had a big ugly solid color set as my background. Changing the background in ‘Appearance Preferences’ and turning off Remote Desktop both fixed nothing. I even rebooted and then rebooted again picking a different kernel. Each time I was presented with the same big black screen. I foamed, I raved, I swore. Anything would have been more tolerable than this.
I finally fixed the problem by launching gconf-editor and then transversing to / -> desktop -> gnome -> background and checking draw_background. All was well after and I went to sleep.