There is a bunch of ways to set an image as your Desktop picture, such as using Quicksilver or using Automator.
Recently, I've found another quick way to do that. Do you want to know what's that?
Not long time ago (around 7-8 months), I've posted an article about How to Set Finder Background which teach you how to set custom image as your Finder background replacing the default solid white color.
Note: Don't see the cute icons, see the solid color background..
But, how if you want to set solid color as your Finder background?