How are backlit aircraft panels (for simulators) made? I'm wondering by which method this sort of aircraft panel that enabling backlighting are made? What is the process? I've gathered they are acrylic but how is the gray paint selectively removed?

pic http://www.simparts.de/WebRoot/Store/Shops/15465782/4B72/6E37/0BF8/50E9/641B/C0A8/28BA/29AA/A320-OHP-009-5.jpg
This video says the following:


  Here's my Tonson TS-3040C CNC making an EFIS panel for my flight
  simulator. For the lettering I am using a 0.4mm End Mill and for
  cutting out I'm using a 1mm End Mill. RPM is 10000 and movement is
  300mm / Min. The material is Cast Acrylic which I have given one coat
  of black paint and two coats of grey paint.


So that's at least one method, but there are probably more...