As someone who uses my Mac every day, I like to customize the **** out of it. This tutorial will explain how to change the color of the selection around the expose selection when you show all windows. I HAVE ONLY TESTED THIS IN SNOW LEOPARD, SO IF YOU ARE A LEOPARD USER, PROCEED AT YOUR OWN RISK.
1. Open a Finder window and hit Command Shift G, which will bring up a Go To Folder window
2. Type (or copy and paste) this into that window: /System/Library/CoreServices/Dock.app/Contents/Resources
3. Inside that folder, search for these items: expose-window-selection-big.png and expose-window-selection-small.png
4. Copy and paste them into a different location (I put them on my Desktop for easy access)
5. Delete the two originals files from the Resources folder
6. Open both of the copied files with any image editor (I used Pixelmator, but Photoshop works too)
7. Change the color to whatever you think would look cool and save the files (DO NOT CHANGE THE NAMES OF THE FILES)
8. Move the edited files back to the Resources folder
9. To view the changes, you will have to end the Dock process: open Terminal and type killall Dock and hit enter
10. After the Dock reappears, activate expose (four-finger swipe or F3 or whatever you use) and you will see your new color
I put a red dot in the middle of the blue color for mine:
Good luck and PM or ask me questions if you have any.