The very blue exterior of Margot in Brooklyn | Margot Amid a stretch of red-brick buildings, the Brooklyn restaurant Margot, right at the corner on a busy intersection, stands out. It’s blue: very blue, its two-story exterior painted the color of a pair of Prue Leith’s glasses, a chore coat worn by a server at a trendy natural wine bar, or a Molly Baz cookbook. During its tenure, Horses, the now-infamous Los Angeles restaurant, was similarly eye-catching: a shock of glossy Yves Klein blue on Sunset Boulevard, the color named for the French artist who made it famous. Across the city, Electric Bleu — which gets its name from the 1987 song by Australian band Icehouse — features a towering panel on its exterior in the same shade, thanks to its owners’ similar affinity for the artist. It projects upward above the restaurant’s entrance, looking, at the right angle, like a lightning bolt has struck life into the otherwise gray-and-brick building. Abroad, some restaurants have taken this very blue trend to its ultimate conclusion. The exterior of Patio, a wine bar in Brighton, England, is painted a blue so saturated that it almost looks fake in pictures. The same goes for the interiors of Berlin’s Cafe Gentil, monochromatic Yves Klein blue from moldings to baseboards. And at Singapore’s Punch Room, everything that isn’t wood, glass, or metal is the same color — a true example of monochromania. (New York City had a place like this, too: the short-lived Only Love…