How to highlight the icon in blackberry?

public final class imagesGridViewScreen extends MainScreen 
{
	GridFieldManager grid;
	LabelField label;
	BitmapField message, call_logs, contacts, internet, calendar, camera, music;
	Bitmap msg, logs, cont, inter, calen, cam, mus;
    public imagesGridViewScreen()
    {            
        setTitle("MENU");
        label= new LabelField(" " , Field.FIELD_HCENTER)
		{
			protected void paintBackground(Graphics g) 
			{
				g.setBackgroundColor(Color.LIGHTGRAY);
				g.clear();
			}
		};
        grid = new GridFieldManager(4 ,4 , 0);
        msg = Bitmap.getBitmapResource("msg.png");
        message = new BitmapField(msg, BitmapField.FOCUSABLE)
        {
        	protected boolean navigationClick(int status,int time)
        	{
        		label.setText("Messages");
        		Dialog.alert("Message icon selected");
        		return true;
        	}
        };
        logs = Bitmap.getBitmapResource("calllogs.png");
        call_logs = new BitmapField(logs, Field.FOCUSABLE)
        {
        	protected boolean navigationClick(int status,int time)
        	{
        		label.setText("Call logs");
        		Dialog.alert("Call Logs icon selected");
        		return true;
        	}
        };
        cont = Bitmap.getBitmapResource("contact.png");
        contacts = new BitmapField(cont, Field.FOCUSABLE)
        {
        	protected boolean navigationClick(int status,int time)
        	{
        		label.setText("Contacts");
        		Dialog.alert("Contacts icon selected");
        		return true;
        	}
        };
        inter = Bitmap.getBitmapResource("internet.png");
        internet = new BitmapField(inter, Field.FOCUSABLE)
        {
        	protected boolean navigationClick(int status,int time)
        	{
        		label.setText("Internet");
        		Dialog.alert("Internet icon selected");
        		return true;
        	}
        };
        calen = Bitmap.getBitmapResource("calendar.png");
        calendar = new BitmapField(calen, Field.FOCUSABLE)
        {
        	protected boolean navigationClick(int status,int time)
        	{
        		label.setText("Calendar");
        		Dialog.alert("Calendar icon selected");
        		return true;
        	}
        };
        cam = Bitmap.getBitmapResource("camera.png");
        camera = new BitmapField(cam, Field.FOCUSABLE)
        {
        	protected boolean navigationClick(int status,int time)
        	{
        		label.setText("Camera");
        		Dialog.alert("Camera icon selected");
        		return true;
        	}
        };
        mus = Bitmap.getBitmapResource("music.png");
        music = new BitmapField(mus, Field.FOCUSABLE)
        {
        	protected boolean navigationClick(int status,int time)
        	{
        		label.setText("Music");
        		Dialog.alert("Music icon selected");
        		return true;
        	}
        };
        grid.add(message, 0);
        grid.add(call_logs, 1);
        grid.add(contacts, 2);
        grid.add(internet, 3);
        grid.add(calendar, 4);
        grid.add(camera, 5);
        grid.add(music, 6);
        grid.setColumnPadding(20);
        grid.setRowPadding(20);
        add(grid);
    }
}