title: JPanel content goes black after opening it from another Jframe
body: <p>So i have a Jframe with a JPanel in it, and there are some buttons on there.
  when a button is pressed it opens up another Jframe with another Jpanel in it, but the content of this Jframe is all black.
  There are supposed to be 4 buttons, and when i open up this second Jframe individually, it shows and works just as it's supposed to.
  Could this ave anything to do with the fact that i used a thread.wait on the second one inside a while(frame.visible)?
  Any help would be greatly appreciated. </p>
  
  <pre><code>import javax.swing.*;
  import java.awt.*;
  import java.awt.event.ActionEvent;
  import java.awt.event.ActionListener;
  
  /**
   * Created by IntelliJ IDEA.
   * User: ThePetr
   * Date: 17/02/12
   * Time: 19:28
   * To change this template use File | Settings | File Templates.
   */
  public class SelectKleurUI {
      private  JFrame frm = new JFrame("Kies kleur");
      private int gekozenKleur;
  
      public SelectKleurUI() {
          frm = new JFrame();
          Toolkit kit = frm.getToolkit();
          GraphicsEnvironment ge = GraphicsEnvironment.getLocalGraphicsEnvironment();
          GraphicsDevice[] gs = ge.getScreenDevices();
          Insets in = kit.getScreenInsets(gs[0].getDefaultConfiguration());
          Dimension d = kit.getScreenSize();
          int max_width = (d.width - in.left - in.right);
          int max_height = (d.height - in.top - in.bottom);
          frm.setSize(Math.min(max_width, 400), Math.min(max_height, 64));//whatever size you want but smaller the insets
          frm.setLocation((max_width - frm.getWidth()) / 2, (max_height - frm.getHeight() ) / 2);
          //frm.setUndecorated(true);
          frm.setResizable(false);
          frm.setVisible(true);
  
          frm.setDefaultCloseOperation(JFrame.DO_NOTHING_ON_CLOSE);
          maakKnoppen();
      }
  
      public  int selectKleur(){
  
          while(frm.isVisible()){
              try {
                  Thread.sleep(100);
              } catch (InterruptedException e) {
                  e.printStackTrace();  //To change body of catch statement use File | Settings | File Templates.
              }
          }
          frm.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
          frm.dispose();
          return gekozenKleur;
      }
  
      public void setKleur(int kleur){
          gekozenKleur=kleur;
          frm.dispose();
      }
      private  void maakKnoppen(){
          JPanel knoppenFrame = new JPanel(new GridLayout(1,0));
          JButton geel = new JButton("Geel");
          geel.setBackground(Color.yellow);
          geel.addActionListener(new ActionListener() {
              public void actionPerformed(ActionEvent e) {
                  setKleur(0);
                  //To change body of implemented methods use File | Settings | File Templates.
              }
          });
          JButton groen = new JButton("Groen");
          groen.setBackground(Color.green);
          groen.addActionListener(new ActionListener() {
              public void actionPerformed(ActionEvent e) {
                  setKleur(1);
                  //To change body of implemented methods use File | Settings | File Templates.
              }
          });
          JButton blauw = new JButton("Blauw");
          blauw.setBackground(Color.blue);
          blauw.addActionListener(new ActionListener() {
              public void actionPerformed(ActionEvent e) {
                  setKleur(2);
                  //To change body of implemented methods use File | Settings | File Templates.
              }
          });
          JButton rood = new JButton("Rood");
          rood.setBackground(Color.red);
          rood.addActionListener(new ActionListener() {
              public void actionPerformed(ActionEvent e) {
                  setKleur(3);
                  //To change body of implemented methods use File | Settings | File Templates.
              }
          });
          knoppenFrame.add(geel);
          knoppenFrame.add(groen);
          knoppenFrame.add(blauw);
          knoppenFrame.add(rood);
          frm.add(knoppenFrame,BorderLayout.NORTH);
  
      }
  }
  
  import javax.swing.*;
  import java.awt.*;
  import java.awt.event.ActionEvent;
  import java.awt.event.ActionListener;
  
  /**
   * Created by IntelliJ IDEA.
   * User: ThePetr
   * Date: 17/02/12
   * Time: 14:55
   * To change this template use File | Settings | File Templates.
   */
  public class Uno {
      private JFrame Hoofdvenster;
      private JPanel pnlOnder=new JPanel(new GridLayout(1,0));
      private JButton[] kaarten=new JButton[50];
      Uno(){
          Hoofdvenster = new JFrame();
          Hoofdvenster.setName("Uno");
          Toolkit kit = Hoofdvenster.getToolkit();
          GraphicsEnvironment ge = GraphicsEnvironment.getLocalGraphicsEnvironment();
          GraphicsDevice[] gs = ge.getScreenDevices();
          Insets in = kit.getScreenInsets(gs[0].getDefaultConfiguration());
          Dimension d = kit.getScreenSize();
          int max_width = (d.width - in.left - in.right);
          int max_height = (d.height - in.top - in.bottom);
          Hoofdvenster.setSize(Math.min(max_width, 800), Math.min(max_height, 600));//whatever size you want but smaller the insets
          Hoofdvenster.setLocation((max_width - Hoofdvenster.getWidth()) / 2, (max_height - Hoofdvenster.getHeight() ) / 2);
          maakComponenten();
          Hoofdvenster.setVisible(true);
          Hoofdvenster.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      }
      private void maakComponenten(){
          for(int i=0;i&lt;7;i++){
              //kaarten[i]=new JButton("Kaart "+i);
              ImageIcon btnIcon = createImageIcon("Images/Naamloos.gif");//new ImageIcon("./Images/Naamloos.gif");
  
              kaarten[i]=new JButton("Kaart "+(i+1),btnIcon);
              kaarten[i].addActionListener(new ActionListener() {
                  public void actionPerformed(ActionEvent e) {
                      //JOptionPane.showMessageDialog(null, "Ok");
                      Hoofdvenster.setVisible(false);
                      SelectKleurUI selectKleurUI = new SelectKleurUI();
                      JOptionPane.showMessageDialog(null, ""+ selectKleurUI.selectKleur());
                      Hoofdvenster.setVisible(true);
  
                  }
              });
              pnlOnder.add(kaarten[i]);
  
  
          }
          Hoofdvenster.add(pnlOnder,BorderLayout.SOUTH);
      }
      private static ImageIcon createImageIcon(String path) {
      java.net.URL imgURL = Uno.class.getResource(path);
  
      return new ImageIcon(imgURL);
  }
  }
  </code></pre>