Java JFrame Hintergrundfarbe ändern

package pack1;

import java.awt.Color;
import java.awt.Image;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.ImageIcon;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JOptionPane;
import javax.swing.JPanel;

public class main extends JPanel implements ActionListener{
   
    ImageIcon icon = new ImageIcon("C:\\Users\\vince\\Pictures\\bilder für game\\memory-karte-hinten.png");
    static ImageIcon icon1 = new ImageIcon("C:\\Users\\vince\\Pictures\\bilder für game\\eule.jpg");
    static ImageIcon icon2 = new ImageIcon("C:\\Users\\vince\\Pictures\\bilder für game\\hund.jpg");
   
   
    JButton button1 = new JButton(icon);
    JButton button11 = new JButton(icon1);
    JButton button2 = new JButton(icon);
    JButton button22 = new JButton(icon2);
    JButton button3 = new JButton(icon);
    JButton button33 = new JButton(icon2);
    JButton button4 = new JButton(icon);
    JButton button44 = new JButton(icon1);
   
    public static void main(String[] args) {
        main main = new main();
        JFrame frame = new JFrame("Game");
        frame.setVisible(true);
        frame.setSize(1000, 1000);
        frame.add(main);
        icon1.setImage(icon1.getImage().getScaledInstance(200,200,Image.SCALE_DEFAULT)); 
        icon2.setImage(icon2.getImage().getScaledInstance(200, 200,Image.SCALE_DEFAULT));
        frame.getContentPane().setBackground(Color.BLUE);
    }
    public main() {
       
        add(button1);
        add(button11);
        add(button2);
        add(button22);
        add(button3);
        add(button33);
        add(button4);
        add(button44);
       
       
       
       
        button11.setVisible(false);
        button1.setVisible(true);
        button22.setVisible(false);
        button2.setVisible(true);
        button33.setVisible(false);
        button3.setVisible(true);
        button44.setVisible(false);
        button4.setVisible(true);
       
       
       
       
       
       
        button1.addActionListener(this );
        button2.addActionListener(this );
        button3.addActionListener( this );
        button4.addActionListener( this );
    }
    public void actionPerformed(ActionEvent ae) {
        Object ob = ae.getSource();
       
        if(ob == button1) {
            button11.setVisible(true);
            button1.setVisible(false);
           
        }if(ob == button2) {
            button22.setVisible(true);
            button2.setVisible(false);
        }if(ob == button1) {
           
        }if(ob == button3) {
            button33.setVisible(true);
            button3.setVisible(false);
        }if(ob == button4) {
            button44.setVisible(true);
            button4.setVisible(false);
        }
       
    }

}