We just finished this little project today!
My husband used one of his 3D printers and made 5 sides of a glowstone block.
Then he spray painted them black (could have used black filament, but we had gray )
I took shrink dink material, figured out the grid and colors and colored it.
Glued the shrinky dink plastic to the inside of each panel.
Using magnets and screws, we attached to the light fixture.