If you are using the default Aero theme you should not edit it you should create a new custom theme so you do not corrupt the original Aero theme, look at the Post #38 of this thread Start menu color change ??
it will show you how to start a new custom theme and then you can edit it. You will need to do 1 of these 2 ways of Enabling custom themes for it to work. Enabling Custom Themes - Windows 7
Or Theme - How to Apply Custom Themes
You will need to edit the Theme.msstyles that you created above the image numbers you will need to edit image # 601, 602, 603, 604, 630, 632, 645, the first four numbers are for the desktop hovers they also remove the hovers in the navigation pane of Explorer the last three numbers remove the hovers from Explorer.
Look at Post #6 of this thread Windows Explorer Properties window background color
will show you how to use a resource hacker to extract and edit and import images into the Theme.msstyles
If you need more help let me know.