@Override
    public void mouseEntered(MouseEvent e) {
        JPanel selectedPanel = (JPanel) e.getSource();
        
        Color x = selectedPanel.getBackground();
        if (x.equals(Color.WHITE)) {
            selectedPanel.setBackground(new Color(50, 50, 50)); 
        } else {
            selectedPanel.setBackground(x); 
        }
    }