I used VHT Nite shades.
I don't recommend that shit at all on a BMW. I sanded and prepped very carefully. But the first coat I freaked out. Instead of an even layer the crap was literally spitting out of the can onto the sidemarker. It made a very blotchy and "dotted" look that only became uniform at about 8 light coats.
They look great from about 4 feet away and you won't notice unless you insepcted them.. but the finished product up close looks like it doesn't belong on a BMW.
I'll try to upload some pics.
I've heard hobby store paint might work better than VHT. You could look in to that. Or a tint shop would be able to wrap them in a film of any darkness, and much more reversible than the Nite Shades.
Here's some pics
One light coat, horrendous coverage.
About 6-7 light coats, terrible look in the right angles
After some clear coats, looks much better because they're still wet (but imperfections still visible up close)