LEDs + superglue + Plexiglas + properly placed paint = RGB edge-lit waveguide pop-culture. Total internal reflection is a nifty arts & crafts tool.
The 'on' photos were made under the same lighting as the first photo, but modern 'superbright' LEDs are, in a word, 'superbright' and they completely blew out the camera even in the face of a direct overhead halogen floodlight. Amazing what 30mA gets you these days.
Add a surrounding layer of 4:1 heatshrink as a combination aesthetic covering and strain relief for the LED wires to prevent the fragile leads from bending at the base. Twist the wire tails... well, because it looks good.
UNTITLED GARDENING PROJECT:LED BONUS STAGE COMPLETE
LEARNED NEW SKILL: FROBNICATE!
PREPARE FOR UNTITLED GARDENING PROJECT: WOOD
Set up each cube for urethane application and 'dome' them.
Any reasonably viscous, clear, two-part urethane adhesive can be used for doming. There are companies (eg, 'RDS Accuflow') that sell doming kits, but you can also get all the necessary bits from McMaster (urethane cartridge, applicator gun and mixer nozzles) and Radio Shack (small refillable butane torch for popping surface bubbles). There's nothing particularly unique in the specialized kits.
There are also companies on the web that will allow you to upload digital artwork to be printed, domed and shipped with a few clicks, ala Cafe Press. I initially tried this route and, unfortunately, found the results to be a little short of mediocre. The resolution was poor, the printing very fuzzy, and the color saturation thoroughly washed out. This is one case where doing it yourself is certain to be faster, cheaper and yield much better results.
Print 1/2"-square 'logos of an appropriate choice' onto translucent white self-adhesive film to be affixed to the face of each cube.
These logos will be backlit so we need to push as much ink into the media as possible to avoid the colors washing out. Hyaz/Papilio brand "inkjet waterproof vinyl" (hyaz.com) is the best choice I've found for high-saturation printing. The Hyaz media is bright, sharp and holds more ink than anything else I've tried. It's easily possible to make the blacks opaque when lit from behind by an arc lamp.
Modern CUPS/Gutenprint drivers have no trouble exerting control over ink deposition density. Slowing down the printing a little with gratuitous use of kill -STOP and kill -CONT also allows the ink time to soak/dry between passes, making it possible to push even more ink into the media without puddling or bleeding.
After printing, spray coat the logos with a clear acrylic topcoat/fixitive. The logo surfaces will be urethane coated later for appearance/durability and the topcoat will prevent the media from outgassing fine bubbles into the urethane during curing. The topcoat also prevents surface damage in upcoming fabrication steps. Krylon 1303 'Acrylic Crystal Clear' is the proper combination of flexible, impermeable and non-yellowing.
After waiting for a full cure on the white paint (7-ish days), coat over the white using heavy black vinyl spray paint as a protective layer. Vinyl paint shrinks dramatically as it cures; use several very light coats to avoid a thick layer that can generate enough skin tension to pull itself up and away from the white paint underneath.
Vinyl spray paint is often sold as 'spray on truck bed liner'. It would probably suck as a bed lining (it's not nearly abrasion resistant enough; it just sort of looks like a real polyethelene liner would), but it's very durable as spray paints go. It's not nearly as durable as powdercoat, but it's much tougher than normal spray paint for those cases where powdercoating isn't practical. Like this one.