A navy crew-neck in lambswool, knitted at a fine twelve gauge, weighs little more than a paperback. It sits close at the shoulder, stops at the belt and has ribbed cuffs that still hold after years of being pushed up the forearm. Of all the knits a man can own, this is the one he will reach for without thinking.
Navy does what black promises and rarely delivers. It is dark enough to look considered, yet soft enough to sit beside brown leather, grey flannel, faded denim or a white oxford shirt without arguing with any of them. It works under a tweed jacket and alone over a T-shirt. Lambswool ages well too: it softens, takes a faint sheen at the elbows and keeps its shape where cheaper yarn goes thin.

how to choose one and keep it
Pinch the knit; it should feel dense and spring back at once. Look for fully fashioned shoulders, the small raised marks where the panels were knitted to shape rather than cut. Pass on anything heavy in acrylic, which pills early and never softens. Wash it rarely, by hand in cool water, and dry it flat on a towel. Fold it, because a hanger pulls the shoulders out of line.
Try one on over a thin shirt, and buy the size that fits at the shoulder, not the chest.