He is not recalled for particularly great leadership, but the late John Lindsay, one of the Mayors of New York City during its decline in the 1960s and 70s, was a well dressed man in a preppy sort of way. And one of the things that both American prepsters like Lindsay and the Italian Loro Piana/Brunello Cucinelli set do well, if I may tar both ethnicities with a generalization, is layer their knitwear.
There are two principal ways to use knitwear in the day's clothes after all. One is as an accent piece, like the lilac vee neck worn under a tweed jacket, and the other is as the focal point. And in that latter role, nothing complements knitwear so well as another piece of knitwear, particularly a lightweight single ply rollneck or mock tee. Wear it under a pub jacket for example, like the version on Mr. Lindsay, to add texture and visual interest to a casual day's clothes.