I had a feeling that this process involved something like cellophane. I like the idea - this could solve the red issue that plagues FLASH as well.

Need to ensure that the lamps behind the 2mm perspex do not make contact / or cause pressure behind the glass. I look forward to the progress !

Haha - I saw the red cellophane done on a Flash actually - it turned the light pink fade into a beautiful deep blood red - when lit.
Yes mate I have numerous 'things to check with this - surely there would be 1.5 -2mm from the lamp tip the BG rear 

I also have to look at how to attach the large sheet of perspex to the BG - AND if it 'bows' in the middle I will sort some type of 'dowel' posts that I will have to ensure wont be seen as well ( as big black dots from the front when lit  )

Will have fun experimenting anyway.