Box never color

[beshoyatef]

Here i mad panel and i put two Boxes in it , then i tried to make a background color for box by useing (background(color.blue) method) but it never has the color .
Then i try to resize its height by useing Box.createRigidArea(new Dimension(10, 50)) but the titleBoard take all the fram
why this?

my code
---------------

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import javax.swing.Box;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JMenu;
import javax.swing.JMenuBar;
import javax.swing.JPanel;
import javax.swing.UIManager;
import javax.swing.border.TitledBorder;

public class MainStegoFrame extends JFrame {

    private JMenuBar bar;
    private JMenu fileMenu, editMenu, toolMenu, helpMenu;
    private JPanel mainPanel;
    private Box displayBox, ButtonsBoxs;
    private JButton loadImageButton, loadVedioButton, loadAudioButton;

    public MainStegoFrame() {
        intializeingMenus();
        intializeingPanels();
        intializeingButtons();
        getContentPane().add(mainPanel, BorderLayout.CENTER);
    }

    public static void main(String[] args) {
        try {
            UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
        } catch (Exception e) {
        }
        MainStegoFrame mainStegoFrame = new MainStegoFrame();
        mainStegoFrame.setDefaultCloseOperation(MainStegoFrame.EXIT_ON_CLOSE);
        mainStegoFrame.setSize(new Dimension(600, 300));
        mainStegoFrame.setLocationRelativeTo(null);
        mainStegoFrame.setVisible(true);
        // mainStegoFrame.setExtendedState(MAXIMIZED_BOTH);
    }

    private void intializeingMenus() {
        bar = new JMenuBar();
        fileMenu = new JMenu("File");
        bar.add(fileMenu);
        editMenu = new JMenu("Edit");
        bar.add(editMenu);
        toolMenu = new JMenu("Tool");
        bar.add(toolMenu);
        helpMenu = new JMenu("Help");
        bar.add(helpMenu);
        setJMenuBar(bar);
    }

    private void intializeingPanels() {
        mainPanel = new JPanel(new BorderLayout());

        displayBox = Box.createHorizontalBox();
        displayBox.setBackground(Color.BLUE);
        TitledBorder titledBorderDispaly = new TitledBorder("Cover");
        displayBox.setBorder(titledBorderDispaly);
        mainPanel.add(displayBox, BorderLayout.CENTER);

        ButtonsBoxs = Box.createVerticalBox();
        ButtonsBoxs.add(Box.createVerticalStrut(30));
        ButtonsBoxs.add(Box.createRigidArea(new Dimension(10, 50)));
        ButtonsBoxs.setBackground(Color.BLUE);
        TitledBorder titledBorderCover = new TitledBorder("Cover");
        ButtonsBoxs.setBorder(titledBorderCover);
        mainPanel.add(ButtonsBoxs, BorderLayout.EAST);
    }

    private void intializeingButtons() {
        loadImageButton = new JButton("Load Image");
        ButtonsBoxs.add(loadImageButton);
        loadAudioButton = new JButton("Load Audio");
        ButtonsBoxs.add(loadAudioButton);
        loadVedioButton = new JButton("Load vedio");
        ButtonsBoxs.add(loadVedioButton);
    }
}

thanks in advance