Ok, start off with 2 cans of NiteShades, 2 cans of whatever clearcoat(I used DupliColor and it worked GREAT), some sand paper(I used 1000 grit wet/dry), windex, paper towels, and cardboard. Here are the steps:
1. Clean both taillights with Windex and dry.
2. Lightly sand both taillights with a high grit sandpaper. I used a little bit of water just to keep the little bits of plastic away from the sand paper and taillights. Try to sand in one direction....front to back, up and down, whatever you prefer but not in circles.
3. After wet sanding clean both tails with water once more and dry with new towels.
4. After they are dry from the water cleaning then clean them one last time with Windex and dry with towels when finished.
5. Lay the cardboard down somewhere in a well ventilated area(preferably a garage) but if you don't have a garage try to get somewhere will dust and particles of debris won't get in the paint. Then lay the two taillights next to each other so you can see both of them when painting so one won't be darker than the other.
6. Spray somewhere between 2-4 very light coats on NiteShades on each tailight, alternating between one taillight then the other. Also you will need to wait about 20-30 minutes before each coat, most people wait about 15-20 minutes so I would guess 20 is a very safe number to wait. After you have finished all the coats with NiteShades take the two taillights into direct light and check to make sure they are about the same in transparency and color, if they aren't add until they are dark enough or wet sand and start over.
7. This is the part that makes the taillights look good and give it a little pop. Now you will add your coats of clearcoat, as I stated earlier I used DupliColor clearcoat, you can use however many coats you deem fit. I used 4 coats of clearcoat and it looks great, but most people that I have talked to used 3 or 4 coats so I would have to say that would be a good number to go with. The rules that applied to the NiteShades apply to this, alternate between each taillight and wait 20-30 minutes before each new coat.
8. You're going to have to let them sit overnight now and finish drying for good. After they have fully dried you will want to clean them one last time with Windex and then inspect them in direct light. Most likely when you inspect them there are going to be some imperfections in the coat seeing as how you haven't done this in a professional paint shop and some particles have found their way onto the paint.
Well now you should have some finished taillights and they should look good if you even somewhat followed these instructions. Well there are some other options that you could try, you can leave two circles of painters tape or almost any tape you wish over the reverse lights so that when you paint the taillights then you still have the full brightness. If you went this route I would think that you should take the two patches of tape off before you clearcoated it so it would be as uniform as possible. Also there are other paints that you can try, I have heard there is another transparent paint in hobby stores, also mixing clearcoat with black paint, and also lastly just strait black paint but I would definately not reccommend doing this because it doesn't have any transparency factor close to the other paints mentioned. Now is the fun part, installing them.....or if you bought some new lights that you have never used yet I guess it's more like trying to install them....but that's another how to.