If you've seen modded TTs chances are you've seen modded headlights. By "modded headlights" I mean people who have removed the side reflector and painted the housing to match the body of the car or just be some different color. Also, many put in clear corners in the process to complete the look.
Here's a side by side shot of what I'm talking about. The closer insert has had the reflector removed, holes filled and has been sprayed to match OEM finish:
That said, European cars don't have side reflectors and S-Line cars have silver housings from the factory. For the rest of us though, there is the headlight mod.
Jeff Bipes has a pretty good outline on how to do this mod:
Keep in mind to get your headlights out you'll have to remove your bumper, which Jeff also has a writeup for:
I myself have done 6-7 sets of inserts myself. I used to sell people modded inserts and then refund them a core charge when they returned their stockers to me, I did about five sets of those for people. However I'm finished with doing that, so now you guys get to hear about the tricks I've learned:
-When applying bondo, get a blob of it on your fingertip and push it through the holes from the back of the insert. Once you have some coming through the hole, smear it around on the face of the insert until you can't make out the hole anymore.
-Let bondo dry for several hours or overnight. Sometimes it can look dry on the surface but be wet inside and really make a mess of things.
-When sanding bondo, use a sanding block until you get really close to where you want to stop sanding. Sanding block takes out bondo much better than hands.
-Use high build filler primer. This stuff is very hard to make run and also helps eliminate any traces of the holes. I'd suggest the orange stuff as it's easier to see where you haven't painted:
-Don't worry if your holes are kinda noticeable. Once they're behind the lenses, they'll be next to invisible.
-As always with liquid paint, use many light, thin coats to get the job done.
-Have extra patience with metallic colors (silver etc). These take a lot more coats. If you grow impatient, you'll end up making the paint run, which with metallics is very noticeable.
-If you do end up with runny paint, let it dry several hours or overnight then sand it down and go again.
-Have so many spare headlight inserts that you can defile one when you're bored in between waiting for coats to dry:
The orange primer. I think this is a pretty cool color actually, it's about the color of terracotta. This is a spare unmodded light (hence the holes) that I tested it on:
When you're really hustlin' headlights: