Change mission control background wallpaper osx lion / mountain lion

This will show you how to change the background wallpaper of mission control in osx lion and mountain lion.

open finder
goto /System/Library/CoreServices/Dock.app/Contents/Resources
find the file defaultdesktop.png
rename it to defaultdesktop_backup.png
copy the image that you want for mission control to the folder and name it defaultdesktop.png
open terminal and type
```
killall Dock
```

now your mission control will have a new background