737 Panel painting/masking question

I understand the process of painting white acrylic grey and then engraving to get the white lettering on the cockpit panels.
I'm stumped with how to mask to create the light grey/dark grey stuff like the fuel panel and packs panel.

Any of you "pros" can share how the masking is done accurately?

http://www.mycockpit.org/forums/atta...id=12486&stc=1

Different ways to do it, but you could spray grey, then mask areas before spraying white then apply lettering.
If you require backlighting you need to be careful the grey coat does not mask out areas you want light to pass through (eg to lettering)