A few of the guys out here in SoCal have had their Crossfire tail lights tinted, and Justin (Z28toXfire) has his pretty darn dark with the white area masked off and still white. I've followed him in bright sunlight and when he puts his foot on the brake pedal you still see a very definite red brake light come on. Just looking at them in daylight you'd think nothing would come through, but they look perfectly normal when the lights come on.

And they look damn good on his white car.