When you are using Expose on Snow Leopard, it puts a blue halo around the window that is currently selected. Here's a hack you can use to change the color of the highlight.

1. Open up a Finder window and go to the /System/Library/CoreServices folder. This is from the root of your hard drive, not your user.

2. Right-click on the Dock application in this folder and choose Show Package Contents. This will open a new Finder window.

3. In the new Finder window go to /Contents/Resources.

4. You then want to copy the expose-window-selection-big.png and expose-window-selection-small.png file onto your desktop. Looking at these files, you can see they contain the "blue glow" images.

5. Open these files in an image editor and adjust the color to something you like.

6. Copy the files from your desktop back to the Finder window they came from. You'll have to select the option to Authenticate, and you'll need to authenticate as root before it'll let you copy the file over.

7. Once the files are copied, you need to restart the Dock before the change will take effect. You can do this by opening a Terminal window and running this command: killall Dock or you can reboot your computer.

Either way, once you restart the blue glow in Expose will be gone and it'll show the glowing color that you created.