Change ImageIcon object transparency (alpha)

My aim is to have multiple panels with images that开发者_StackOverflow中文版 have alpha channels (transparent parts) on top of each other. So I followed the code in this site http://tinyurl.com/m27exs. It worked the way I wanted it. It had two ImagePanel objects on top of each other with the top-most having an alpha channel (transparent part).

Now my problem is how I can change the transparency (see-throughness?) of the ImageIcon objects inside that ImagePanel class?

Check out Darryl's Alpha Icon.