Color

import java.awt.Color;
import java.awt.FlowLayout;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;

/**
 *
 * @author onezer0
 */
public class Cores extends JFrame {

    public Cores() {
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setSize(300, 120);
        setLayout(new FlowLayout());
        setBackground(Color.yellow);

        JPanel panel1 = createColoredPanel(Color.red);
        JPanel panel2 = createColoredPanel(Color.blue);

        addButtonsToPanel(panel1);
        addButtonsToPanel(panel2);

        add(panel1);
        add(panel2);
    }

    private JPanel createColoredPanel(Color color) {
        JPanel panel = new JPanel();
        panel.setLayout(new FlowLayout());
        panel.setBackground(color);
        return panel;
    }

    private void addButtonsToPanel(JPanel panel) {
        panel.add(new JButton("p1"));
        panel.add(new JButton("p2"));
        panel.add(new JButton("p3"));
    }

    public static void main(String[] args) {
        Cores cores = new Cores();
        cores.setVisible(true);
    }
}