Constance Belt Buckle & Reversible Leather Strap 38 mm Box 135 and Togo Calfskin So Black Metal Finish Buckle Noir Bleu De Prusse

Prussian blue has always been the diplomat of colours — dark enough to pass for black in dull light, blue enough to feel like a choice when the sun lands on it. On the reverse of this Constance strap it is a small pleasure most people never see, which is half the point of owning it.

The formula is the familiar one done well: Box calf over pebbled Togo at thirty-eight millimetres, the black face formal and glassy, the Bleu de Prusse face softer under its pebbled grain. Worn dark side out, it is the belted suiting companion; flipped, it gives navy trousers and grey flannel a depth of colour that a plain black strap cannot match. The So Black buckle keeps the metal conversation muted, its blacked-out finish working away under the radar.

I like this one for navy-on-navy dressing — blazer, deep trousers, the belt blade just catching light, all of it reading as one tonal study. It also handles the office-to-dinner slide better than most accessories: no change needed, just a flip on the way out of the building.

An honest limitation: because the reverse is blue rather than a neutral, this is less of an everything-belt than its brethren — it plays best with cold tones, and against a wardrobe built on browns and warm greys the blue will look like a guest rather than a host. Size it carefully off your measured waist, 80 to 115 in centimetres, and keep the smooth Box face away from rough chair backs, which is where dark smooth leathers take most of their scars.