I've been looking for a solution to this problem, and found it in the Compiz Control Centre. There is an option there to check to see if NumLock is on or off and adjust the colors accordingly. It's always been highly customizable to me, while still being very beautiful looking. I'd call it a complete solution.
You can install it from Lucid either by installing or going into Additional Drivers. Just enter a PPA in the software repository and 50e0806aeb orvivick