Am I right in thinking the background was originally mirrored? If so then I guess you could've used a thin piece of polished alloy sheet or plastic mirror etc. behind the glass to replicate this; though problematic if you want light to shine through in various places.
As for the need to paint the background white behind the decals, I prefer to use the water decal paper that comes in white or clear. It has a perfect opacity for replicating silk screened graphics like pinball plastics etc. that need to be backlit but also makes the graphics colour pop when printed.
As for the need to paint the background white behind the decals, I prefer to use the water decal paper that comes in white or clear. It has a perfect opacity for replicating silk screened graphics like pinball plastics etc. that need to be backlit but also makes the graphics colour pop when printed.