“Conundrum,” the episode of “Star Trek: The Next Generation” in which everyone gets their memories erased and Data thinks he’s a bartender, is one of the series’ best. He makes this drink for Troi after losing a game of 3-D chess. It goes from clear to green to red in the blink of an eye. We don’t yet have the technology to recreate that marvel, but we can mimic it using a trick with red-cabbage-infused rum. The drink will turn from purple to red with the addition of the fruit juices.