when I did mine with vinyl i bought the "dark smoke" from rvinyl.com. It's pretty easy to use. Below I have a link to a tutorial I did on how to apply it.
The downside to it I've noticed that, depending where you live, weather condition will cause it to discolor and fade.
http://vimeo.com/7099259
I've since used Niteshade on my tail lights and I like it much better. Only downside to that is if you get hassled by the police about it, you can't just remove it, you have to sand it all off.