When a non-opaque popup menu is shown, the opaque property is not honored. In the following example, the menu items and the popup menu containing these items are made non-opaque. Therefore, the red background should shine through.

=====START test.java=====
import javax.swing.*;
import javax.swing.event.*;

public class test {
  public static void main(String[] args) {
    JFrame f = new JFrame("Popup Menus");
    f.getContentPane().setBackground(java.awt.Color.RED);

    JMenuBar bar = new JMenuBar();
    JMenu menu;
    JMenuItem item;
    
    bar.add(menu = new JMenu("File"));
    menu.add(item = new JMenuItem("New"));
    item.setOpaque(false);
    menu.add(item = new JMenuItem("Open..."));
    item.setOpaque(false);
    menu.add(item = new JMenuItem("Save"));
    item.setOpaque(false);
    menu.add(item = new JMenuItem("Save As..."));
    item.setOpaque(false);
    f.setJMenuBar(bar);
    
    menu.getPopupMenu().setOpaque(false);

    f.setSize(new java.awt.Dimension(640, 480));
    f.setVisible(true);
  }
}
====END test.java====
###@###.### 2005-05-25 18:22:19 GMT