So far you should have something that looks like this.
Up next is painting the numbers on the lens, this is where it starts getting a little tricky, but not impossible by no means.
Start by cleaning the side to be painted. I use Dawn dish soap, and clean it good so that the paint will stick properly. Then, once you've marked the front side so you know where to put the mask, hold the lens up to some light and line it up on the inside of the lens. I used some tape to hold it in place.
Once it's exactly where you want it, tape the bottom so it cannot move.
Fold it back at the tape and remove the backing.
Then carefully put it on the lens, starting at the bottom and working your way up.
Once it's on the numbers should match up with the marks made on the front side of the lens.
Then carefully pull the backing away.
THis is the paint I use. It's just green and white. It takes some time to get the right color, but these two colors will do it.