An interior designer with stern opinions visited us recently. All was well until he spotted our cushions. His brow furrowed. “I would never do that,” he muttered. The issue was the piping. I had chosen scarlet to cheerfully offset the blue cover. Among cushion purists, such jaunty juxtapositions are not done. I had committed a design crime.

This got me thinking. If a trim could cause such offence, what other unspoken etiquette made, as British author and socialite Nancy Mitford might have put it, one cushion “U” [upper class] and another “non-U”? And how to avoid further stylistic booby traps?

Financial Times