One of my buddies put led's in his headligner, and neon on the sub, and replaced all the bulbs in the dash with matching colors. He's got it wired so that the led's and neon come on when you open the door, and the neon is on a 3 position switch so it will come on with the doors, turn off, or be turned on all the time.
IMO, it looks preety cool with his blue truck when he opens the door and it all lights up blue. It can be a cool custom touch.