Kevin, the way it is done is to have 2 different icons - one for normal display and another one that is displayed on what is called a "mouseover event", so it would be easier just to have the larger icon without the hocus-pocus (otherwise known as overhead) to change it dynamically.
Chris, I thought it was my geriatric eyes, but I cannot make out what those icons are, or even differentiate between them - they are all teensy green blobs to me. Perhaps if they were a different color, with sharper contrast, it would be enough. Also, when you mouseover them, you do see the text of what they are, which is a great help.