Jtogglebutton setting background dynamically

i have a problem with setting background color of Jtogglebutton dynamically. I want Jtogglebutton blink like a led, on and off at a decised time, like 500ms. I tried to override paint and paintComponent method too. But couldn't succeed either. I'm stuck. Here is my code thanks for help.

Led class:

public class Led extends JToggleButton {
private Color okColor = Color.GREEN;
private Color notOkColor = Color.RED;
private static int BLINK_FREQUENCY=500;

public Led() {
    this.setPreferredSize(new Dimension(50, 50));
    timer.start();
}

Timer timer=new Timer(BLINK_FREQUENCY, new ActionListener() {

    @Override
    public void actionPerformed(ActionEvent e) {
            setBackground(okColor);
            System.out.println("ok");
            try {
                Thread.sleep(BLINK_FREQUENCY);
            } catch (InterruptedException e1) {
                e1.printStackTrace();
            }
            setBackground(notOkColor);
            System.out.println("notok");
    }
});

}

MainFrame Class:

public class MainFrame {

private JFrame frame;
private Led led;
private JPanel panel;

public MainFrame() {
    initializeComponents();
}

private void initializeComponents() {
    frame = new JFrame("Blinking Led");
    frame.setSize(400, 400);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setLocationRelativeTo(null);
    {
        panel = new JPanel();
        led = new Led();
        panel.add(led);
        frame.add(panel);
    }

}

public void setVisible(boolean visible) {
    frame.setVisible(visible);
}

}

I don't see the point in using the Timer class but just a simple thread should work

public Led() {
    this.setPreferredSize(new Dimension(50, 50));
    thread.start();
}

Thread  thread  = new Thread(() -> {
                    while (true) {
                        if (getBackground().equals(notOkColor)) {
                            setBackground(okColor);
                        } else {
                            setBackground(notOkColor);
                        }
                        try {
                            Thread.sleep(BLINK_FREQUENCY);
                        } catch (InterruptedException e) {
                            e.printStackTrace();
                        }
                    }
                });