Java JPanel set background

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JTabbedPane;


public class Main {
  public static void main(String[] args) {
    JFrame frame = new JFrame();
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setTitle("Tabbed frame");
    //from ww w. ja  v  a  2s .co m
    JTabbedPane cardTabs = new JTabbedPane();
    cardTabs.setPreferredSize(new Dimension(300, 400));
    
    JPanel bluePanel = new JPanel();
    JPanel redPanel = new JPanel();
    bluePanel.setBackground(Color.blue);
    redPanel.setBackground(Color.red);
    
    cardTabs.add(bluePanel, "BLUE PANEL");
    cardTabs.add(redPanel, "RED PANEL");
    
    frame.getContentPane().add(cardTabs, BorderLayout.CENTER);
    
    frame.pack();
    frame.setVisible(true);
  }
}