An off-topic question regarding basic Java Programming

[tr4nquility]

Hello. I know that this is a board for emulation news, specifically JPCSP.
However, since it is using Java as primary language, I would like to ask a little thing on Java programming, hoping some users with knowledge of Java can help me out..
(To moderators : please feel free to delete this thread if it is inappropriate in any ways ^_^ )

Here's my problem description :
I would like to build a simple highlighter program. The idea is to set an image to change the cursor so that it will look like a highlighter. And then, when we move the cursor, it will trace a line along with our movement. The requirement here is to be able to draw the line on a transparent background (not fully transparent though, just about 55% and the line itself should be fully opaque).

My progress so far is being able to draw the line, with transparent background. However, the line is also transparent. Here's my code : left click to begin drawing, right click to stop, and press space to change color.

Code:

import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Point;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import java.awt.event.MouseMotionListener;

public class FreehandExample extends JFrame implements MouseListener, MouseMotionListener, KeyListener {
     private int counter = 0;
     private int draw = 0;
     private int red[] = {58,71,231,243,255};
     private int green[] = {54,224,235,109,40};
     private int blue[] = {241,95,61,52,40};
     private Point start, end;
     private Graphics gd;

     public FreehandExample()
     {
        setUndecorated(true);
        setBackground(new Color(255,0,0));
        setSize(new Dimension(300,200));
        setLocationRelativeTo(null);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        addKeyListener(this);
        addMouseListener(this);
        addMouseMotionListener(this);
        setOpacity(0.55f);
        setVisible(true);
     }

    public void mousePressed(MouseEvent e) {
        start = new Point(e.getX(), e.getY());
    }
    public void mouseClicked(MouseEvent e) {
        if(e.getButton() == MouseEvent.BUTTON1) draw = 1;
        if(e.getButton() == MouseEvent.BUTTON3) draw = 0;
    }
    public void mouseEntered(MouseEvent e) {}
    public void mouseExited(MouseEvent e) {}
    public void mouseReleased(MouseEvent e) {}
    public void mouseDragged(MouseEvent e)  {}

    public void mouseMoved(MouseEvent e) {
       gd = this.getGraphics();

       if(draw==1){
          end = new Point(e.getX(), e.getY());
          gd.setColor(new Color( red[counter],green[counter],blue[counter]));
          gd.drawLine(start.x, start.y, end.x, end.y);
          start = end;
       }
    }

    public static void main(String []args){
         new FreehandExample();
    }

    public void keyPressed(KeyEvent e) {
         if(e.getKeyCode() == KeyEvent.VK_SPACE) {
            counter++;
            if(counter>4) counter=0;
         }
    }
    public void keyReleased(KeyEvent e) {}
    public void keyTyped(KeyEvent e) {}
}

I have tried the concept of per-pixel transparency (as referrred in here)... but the line is not being drawn immediately... there is some kind of delay before the line is drawn. However, it indeed produced the correct result e.g the line is not transparent while the frame is transparent.

The second idea is to capture screenshot using Robot class, and then apply it as frame background in fullscreen. This way we will have a window as being "transparent".. Though when we have a video working in background, this method will definitely fail.. Even if we set the program to take screenshot every seconds, it's still not a good way to achieve transparency...

Could someone please help me modify this code (or at least give some insights ^_^ ) to meet the requirement...?

Thanks.