JPanel

Client properties:
Size styles:

General

In order to properly display JTabbedPane's with Panther design, Quaqua sets all JPanel's to non-opaque. Thus changing the background color of a JPanel has no effect, unless you explicitly call setOpaque(true) on the JPanel.

myPanel.setOpaque(true);

If your application logic relies on JPanels being opaque by default, you can set the UIManager property Panel.opaque to Boolean.TRUE.

UIManager.put("Panel.opaque", Boolean.TRUE);

Tip: You can set a TitledBorder on the JPanel, to draw a NSGroupBox.