I have several desktops. When I am doing serious color work with a scanner and Photoshop, I do an all-grey background. When I am logged in as root or administrator, it is a bright yellow. Annoying-- yes, but then again I want to remind myself that I am in as God, and to be honest, it is not often at all! If I have to access my servers over modem or vnc, it is also grey.
My primary linux one is the one with the planet, and my primary Mac one is the Enterprise. The Windows desktop has the one with the dolphin.