Having it set to whatever the title bar color might not be a bad idea, or automatically a set shade darker then the default GTK window color.
So if the window grey is of a different tone the bars background will match the color and set to a slight shade darker.
Having it set to whatever the title bar color might not be a bad idea, or automatically a set shade darker then the default GTK window color.
So if the window grey is of a different tone the bars background will match the color and set to a slight shade darker.