Solid white menu bar
sudo defaults write /System/Library/LaunchDaemons/com.apple.WindowServer ‘EnvironmentVariables’ -dict ‘CI_NO_BACKGROUND_IMAGE’ 1
Grayish menu bar
sudo defaults write /System/Library/LaunchDaemons/com.apple.WindowServer ‘EnvironmentVariables’ -dict ‘CI_NO_BACKGROUND_IMAGE’ 0
Translucent menu bar
sudo defaults delete /System/Library/LaunchDaemons/com.apple.WindowServer ‘EnvironmentVariables’
restart/
source: http://www.usingmac.com
