I'm so happy, I found this solution over at maxosxhints, and it works!
Type this in Terminal and restart (oh, and never mess with system files without proper backup and all that
):

Type this in Terminal and restart (oh, and never mess with system files without proper backup and all that
Code:
sudo defaults write /System/Library/LaunchDaemons/com.apple.WindowServer 'EnvironmentVariables' -dict 'CI_NO_BACKGROUND_IMAGE' 1