My car had them when I bought it and I can say from experience DON'T DO IT! Tinted headlight covers will have to be removed every time you drive at night unless you're a complete idiot, and you will get pulled over for tinted taillight covers... I did. Needless to say the covers stayed less than a year after I bought the car.
I've been considering CLEAR headlight covers now, just to keep the bugs out of the headlights, but I would never do tinted or fogged covers ever again. The taillight covers look like crap anyway, IMHO, and if you really like the blacked out look, go with an aftermarket set of lenses, not covers.