how to paint clear plastic? Answered

You will need to use glass tinting film.  For painting the rest, you should use vinyl dye (e.g., VHT) in whatever colors you want.

an easier way will be putting tin foil on the plastic and paint it

If the face panel is curved but not a compound curve you can laminate a colored plastic film on it .

the letters a through z are not keywords in your question.

The 'paint' you're referring to on most visual lenses is a microscopically thin layer of metals chemically coated on the lens. There aren't any cheap consumer grade solutions to do this yourself. You'll probably want to buy a lens already coated that you can cut to fit (snowboard mask comes to mind).

http://en.wikipedia.org/wiki/Dichroic_filter