change progress bar colore

import java.awt.*;
import javax.swing.*;

public class ProgressBar extends JFrame {

	JProgressBar current;
	int num = 0;

	public ProgressBar() {

    	setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    	JPanel pane = new JPanel();

    	pane.setLayout(new GridLayout());
    	current = new JProgressBar(0, 100);
    	current.setValue(0);

    	current.setStringPainted(true);
    	pane.add(current);
    	setContentPane(pane);

	}

	public void iterate() {
    	while (num < 1000) {
        	current.setValue(num);
        	if (current.getValue() == 20) {
            	current.setForeground(Color.RED);
        	} else if (current.getValue() == 50) {
            	current.setForeground(Color.ORANGE);
        	} else if (current.getValue() == 100) {
            	current.setForeground(Color.GREEN);
        	}
        	try {
            	Thread.sleep(5000);
        	} catch (InterruptedException e) {
        	}
        	num += 10;
    	}
	}

	public static void main(String[] arguments) {
    	ProgressBar frame = new ProgressBar();
    	frame.pack();
    	frame.setVisible(true);
    	frame.iterate();
	}
}