comboBox.setBackground(null); comboBox.setFont(null); comboBox.setForeground(null);
if (comboBox.getForeground() instanceof UIResource) comboBox.setForeground(null);  if (comboBox.getBackground() instanceof UIResource) comboBox.setBackground(null);
  protected void uninstallDefaults()  {    UIDefaults defaults = UIManager.getLookAndFeelDefaults();    comboBox.setBackground(null);    comboBox.setFont(null);    comboBox.setForeground(null);    shadow = null;    darkShadow = null;    lightHighlight = null;    highlight = null;  }