Solidifying the Menu Bar in Leopard
From Mac Guides
With Mac OS X Leopard on newer computers the menu bar is transparent. With 10.5.2 or later this option can be configured from System Preferences>Desktop and Screensaver>Desktop, by unticking the "Translucent Menu Bar" option.
However if you want further control over your menu bar's transparency you can still follow the steps below. Note in 10.5.2 or later you must have "Translucent Menu Bar" ticked for the options below to take affect. You do this with a Terminal command.
sudo defaults write /System/Library/LaunchDaemons/com.apple.WindowServer 'EnvironmentVariables' -dict 'CI_NO_BACKGROUND_IMAGE' 1
This makes the menubar completely white.
Alternatively you can get a menubar that looks similar to how it looked in Mac OS X Tiger by replacing 1 with 0.62 i.e. by typing:
sudo defaults write /System/Library/LaunchDaemons/com.apple.WindowServer 'EnvironmentVariables' -dict 'CI_NO_BACKGROUND_IMAGE' 0.62
After doing this you will need to restart your Mac for the changes to take effect.
Note that an admin password is required to make this change. In order to return to the default menu Leopard menu bar:
sudo defaults delete /System/Library/LaunchDaemons/com.apple.WindowServer 'EnvironmentVariables'