Boards are assembled using small, 0604 red LEDs as that's what I had on hand. Pics:
Assembly
Front illuminated
External
The test worked well as far as illumination, however, I don't believe the LEDs I'm using can light up an area this large. This test would work better with smaller illuminated areas.
The Shitty Add-On movement continues on, and there are more and more boards featuring reverse-mounted LEDs. Reverse-mounted LEDs don't lend themselves to pick and place assembly, so this is a project to see if another technique can be used (Oreo construction) to make flat, illuminated panels in PCBs.