Helper method to create the Synthetica background color with alpha value
provided by client properties "Synthetica.background" and
"Synthetica.background.alpha".
Returns true if toplevel popup menu handling is enabled and the invoker
is a toplevel JMenu (or marked by client property "Synthetica.menu.toplevel")
or popup is marked as toplevel popup by client property "Synthetica.popupMenu.toplevel".