The green box?

K. I know this sounds wierd. But there is a green border around my scroll pane.
Go to and look at the scroll pane on the front page. When it is idle there is nothing. But move it up and down and you will see this wierd green border surround the pane.

I have no clue what that is. It completly boggles me to where that came from and why it is there. Any help why this dreaded thing is there?