To say the Colbans like to keep a low profile is an understatement. “We tend to decline a lot of things,” says Jean-Claude. He and his sister are seated in leather chairs in their father’s former office, which is lined with books and ephemera such as Champagne-shaped bottles of Charvet detergent. They say no to most interviews and don’t have much to say on the subject of their personal lives. (All I came to know after spending several days there was that Jean-Claude has a son who may one day come to work for them and that Anne-Marie lives somewhere on the Left Bank.) They are also loath to discuss their notable clientele, past and present. “We don’t like to play favorites,” says Jean-Claude, who works on designs. “We enjoy making them shirts. And that’s what’s important, our relationship with the clients,” says Anne-Marie, who works with customers. Charles de Gaulle’s own measurements.Photographer Jonas Unger. People with money and power have long been fitted for shirts from Charvet. So while sultans, pashas, and princes have …