popupMenu.setOpaque(true);
  public void installDefaults()  {    UIDefaults defaults = UIManager.getLookAndFeelDefaults();    popupMenu.setBackground(defaults.getColor("PopupMenu.background"));    popupMenu.setBorder(defaults.getBorder("PopupMenu.border"));    popupMenu.setFont(defaults.getFont("PopupMenu.font"));    popupMenu.setForeground(defaults.getColor("PopupMenu.foreground"));  }