12.04: How do I change background color of Main Menu in Gnome Fallback?

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http://askubuntu.com – When running in Gnome Fallback mode (Gnome Classic) in Ubuntu 12.04, I added the Main Menu to the bottom panel, but I have a problem with the customization of its colors. It is like the old Gnome 2 menu that combined Applications and Places into one. By default with the Ambiance theme, the menu's background is white when it should match the background of the panel itself. When using the Applications/Places menu that is enabled by default, it has the proper background matching the panel as it should. Is it possible to customize the Main Menu's background color in Gnome Fallback or is the sett (HowTos)