You could use a row of the individual LED "dots" available @ most auto parts stores...just drill the appropriate size hole in an evenly spaced row, press em' in & wire em' up.

However...if you use any other color than amber/yellow in front(forward facing), & red in the rear(visible from the rear), you are giving Mr. Police Officer a "freebie" when it comes to reasons to pull you over...yes, that's personal experience.