Food trends go hand in hand with Instagram. Starbucks’ Purple and Pink drink blew up in part because people love tasting and posting about cool foods and drinks. There’s rainbow everything these days. Does it taste good? Maybe. Does it look great on Instagram? Hells yes. This summer’s biggest hashtag is turning out to be from the dark side. From New York to Moscow to the beaches of Bali, black ice cream is dominating foodie threads.