I have heard about people spraying their tails to get them dark. I dont think I would trust my hand to do it but my friend did it to his cars and they look great. I know you can buy the paint for it almost any were (car supply places) but again I dont know that I would do it to mine. Here are a few DIY links I found for you:
This one is not a jetta but the lights look nice and the instructions are highly detailed:
http://www.350z-tech.com/zwiki/How_to_Smoke_Taillights
http://members.tripod.com/~Jetta_GLi/taillights.txt
This one is not a jetta but the lights look nice and the instructions are highly detailed:
http://www.350z-tech.com/zwiki/How_to_Smoke_Taillights
http://members.tripod.com/~Jetta_GLi/taillights.txt