I'm running Xubuntu 12.04 and using the Unity greeter with LightDM. Everything works well except for I can never change the background. I've tried editing the .conf file, editing the gsettings as the lightdm user, even compiling an override file for com.canonical.unity-greeter. All of these fail, and I end with a dark purple background. I was able to get rid of the grid using gsettings, but that's about it. I've enabled switching user backgrounds, but that never works. I'm wondering whether this is Xfce/Xubuntu specific, or a bug.