If you need to develop with Xcode 4 alongside Xcode 5, here is a simple icon replacement for Xcode 5. I use it to discriminate my two Xcode on the sidebar or in the tab switcher.
Just copy the modified Xcode.icns file into
/Applications/Xcode.app/Contents/Resources/ and go!
You will need, of course, to have your two versions of Xcode at different places, as I describe it in Xcode 4.5 and 4.4.1 Cohabitation. If you want to revert to the original Xcode icon, just use Xcode.icns (original).
And if you want to celebrate the new shiny iPhone 5c, here is some variations with the Xcode 5c icons:
Rename the icon file name to
Xcode.icns and drop it in
/Applications/Xcode.app/Contents/Resources/. Happy coding!