Created this for a large scale RGB 8x8 matrix project, I've also included smaller 4x4 versions to fit other printers. There are two versions of each size, one for 5mm round LEDs and the other for 5050 style square LEDs found on flexible strips.

This will be used with some individually addressable RGB LED strips (generic Digital Dream variants found on Amazon) cut down and mounted on the back. I have some frosted lighting film for the front (Roscolux 116) that will be attached with VHB double sided tape. Since the strips were about $12 per meter I can build each matrix for about $20, far less than what comparable 8x8 matrix panels I've found. Controller will likely be a Teensy 3.1, since the strips are designed to be connected end to end it should allow me to control a bunch of these panels with one device.

I'll refresh this with photos as the project progresses. Enjoy!

Single cell and 8x8 SCAD files created. First time using OpenSCAD so maker beware!

UPDATE: Added new version that should match most 60 LEDs per meter strips (16.667mm apart). Requires far less cutting and soldering, thickness reduced to 12.7mm. Strips can be secured directly to the back, this will allow you to build edge-to-edge matrix displays with 8 running strips.