How about this:

Put a panel mount bi-color (blue/red) LED in the hole in the door.
Run the blue from an acoustic dance-with-the-beat kinda circuit,
Run the red from a faux security flasher circuit, when the key is out.

Does this sound feasible or crazy? Any thoughts about how this could be done or where supplies would be available? If possible it'd also be nice to get wired LEDs, rather than those with just bare leads (like on the right in the pic below).

 

you could always run the LED through a potentiometer to your speaker. Just set the potentiometer up so the door speaker power can't max out the LED. Play something loud and watch the LED while setting the pot.