I have designed a couple luminaries before (several years ago), but this time I decided to put the design on the inside. I started with plain white Elephant Hide paper and painted one side a mottled green/blue. Then, I drew the black pattern on the same side of the paper with a marker. Since the painted side is on the inside, the design only appears when the luminary is lit from the inside.
Here are a couple more views of the bottom of the piece to show how this works:
