it's not legal
i smoked my tails back in 2005 i think, now it's still slightly dark, but i never got any problem. i didnt make them go black neither lol. but nowadays with begin and his friends, watch out
one thing you need to make sure of, is that the reflectors still do their job and that your lights are clearly visible (when on) from about 150ft. some people make them sooooo dark you can barely see them light on even during the night :/