The L&F drawPopupMenuBackground method draws a border around the popup menu, but only on Windows (and I suppose Linux too):
#if ! JUCE_MAC g.setColour (findColour (PopupMenu::textColourId).withAlpha (0.6f)); g.drawRect (0, 0, width, height); #endif
What is the purpose of this border? My guess is that the dropshadow that is applied to the menu cannot be reliably applied on Windows, so the border is a way of ensuring that the menu has sufficient contrast with its background?