JButton sin fondo?

[g17ecu]

public class JavaTest extends JFrame {

private JButton btnTest = new JButton();
private JPanel rootContainer = new JPanel(new FlowLayout());

public JavaTest() {
super("Java Test");
setSize(400, 400);
setLocationByPlatform(true);
setDefaultCloseOperation(EXIT_ON_CLOSE);
setContentPane(rootContainer);

prepareButton();

rootContainer.add(btnTest);
}

private void prepareButton() {

btnTest.setOpaque(true);
btnTest.setBorder(null);
Color c = UIManager.getLookAndFeel().getDefaults().getColor( "Panel.background");
btnTest.setBackground(new Color(c.getRed(), c.getGreen(), c.getBlue()));
btnTest.setIcon(new ImageIcon(getClass().getResource("/ecuador.png")));
}

public static void main(String args[]) {
new JavaTest().setVisible(true);
}
}