Backdrop 4+‎

Backdrop is a simple utility to fill your screen with a giant blank window. Fill the window with a solid color or a custom image, your choice. ALSO, includes a Fullscreen Color Cycle mode to see various colors filling your displays.

Backdrop received a 4 Mouse Rating by Macworld

Backdrop is useful for:
* Screenshots - take screenshots of one or many windows without having to clean up your desktop
* One thing at a time - Use Backdrop in between applications to let you focus on a few windows at a time. Want just one window of an app? Switch to Backdrop, then use Expose to pick out the window.
* Web design - create a full size image with outlines of more common screen sizes to help to check how your pages will look on different monitors
* Fullscreen Color Cycle - run the Cycle to see red, green, blue, white, and black from corner-to-corner on your displays.

Features:
* Supports multiple displays
* Set a color or a custom image
* Fullscreen Color Cycle mode
* Remains in the background during Exposé
* Works well with Spaces