import java.awt.Color;
import java.awt.GridLayout;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;

import javax.swing.JFrame;
import javax.swing.JPanel;

public class PanelArray extends MouseAdapter {
    static Color[] colors = { Color.RED, Color.BLUE };

    public static void main(String[] args) {
        new PanelArray().run();
    }
    
    void run() {
        JFrame frame = new JFrame();
        frame.setLayout(new GridLayout(3, 3));
        for (int i = 0; i < 3; i++) {
            for (int j = 0; j < 3; j++) {
                JPanel panel = new JPanel();
                panel.setBackground(colors[(i + j) % 2]);
                panel.addMouseListener(this);
                frame.add(panel);
            }
        }
        frame.pack();
        frame.setVisible(true);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    }

    public void mouseClicked(MouseEvent event) {
        JPanel panel = (JPanel)event.getSource();
        Color color = panel.getBackground();
        System.out.println(color == Color.red ? "RED" : "BLUE"); 
    }
}