Help me optimize jtextpane

Provided a working class with mainfile (StillLife), all it does is it writes out a with 2 diffrent colors to a text pane, and in System.out print out the time it took to write those a's out. As you can see it's very slow ): Need another aproach to solve this problem, please help!

What i would like to do is connect a telnet stream to this, but as you know telnet uses ansi color codes
and with this slow colored text performance of the jtextpane it  results in a slow telnet application.

output from system out...
Execution took:625 ms
Execution took:1140 ms
Execution took:1687 ms
Execution took:2031 ms
Execution took:2780 ms
Execution took:3531 ms
Execution took:3983 ms
Execution took:4609 ms
Execution took:750 ms
Execution took:406 ms
Execution took:1062 ms
Execution took:1718 ms
Execution took:750 ms
Execution took:2421 ms
Execution took:3593 ms

//Code start here
//----------------------------------------------------------
// ColorPane.java
// A simple extension of JTextPane that allows the user to easily append
// colored text to the document.
//

import java.io.InputStream;
import java.io.PrintStream;

import java.util.*;

import org.apache.commons.net.telnet.TelnetClient;

import javax.swing.*;
import javax.swing.text.*;
import java.awt.Color;

public class StillLife

    extends JTextPane {
  private TelnetClient telnet = new TelnetClient();
  private InputStream in;
  private PrintStream out;
  private StringBuffer sbBuffer = new StringBuffer();


  public StillLife (){
   sbBuffer.append("a ");
   final Random generator2 = new Random( 121 );
    System.out.println( generator2.nextBoolean());
    Thread thread = new Thread() {
    public void run() {
     
      int number = 0;
      while(true)
      {
       
        try {
          Thread.sleep(3000);
        }
        catch (InterruptedException ex) {
          System.out.println(ex.toString());
        }
         long start = System.currentTimeMillis();
        number = 0;
            while (number++ < 400){
              if(generator2.nextBoolean())
              append(Color.red, sbBuffer.toString());
            else
                append(Color.green, sbBuffer.toString());
            }
            System.out.println("Execution took:" + (System.currentTimeMillis() - start) + " ms");
      }
    }
  };
  thread.start();

  }


  public void appendNaive(Color c, String s) { // naive implementation
    // bad: instiantiates a new AttributeSet object on each call
    SimpleAttributeSet aset = new SimpleAttributeSet();
    StyleConstants.setForeground(aset, c);

    int len = getText().length();
    setCaretPosition(len); // place caret at the end (with no selection)
    setCharacterAttributes(aset, false);
    replaceSelection(s); // there is no selection, so inserts at caret
  }

  public void append(Color c, String s) { // better implementation--uses StyleContext
    StyleContext sc = StyleContext.getDefaultStyleContext();
    AttributeSet aset = sc.addAttribute(SimpleAttributeSet.EMPTY,
                                        StyleConstants.Foreground, c);

    int len = getDocument().getLength(); // same value as getText().length();
    setCaretPosition(len); // place caret at the end (with no selection)
    setCharacterAttributes(aset, false);
    replaceSelection(s); // there is no selection, so inserts at caret

  }

  public static void main(String argv[]) {

    StillLife pane = new StillLife();
    JFrame f = new JFrame("ColorPane example");
    f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    f.setContentPane(new JScrollPane(pane));
    f.setSize(600, 400);
    f.setVisible(true);



  }

    }

//Code ends here
//----------------------------------------------------------