One of the best parts of autumn, besides the crisp air, is the chance to get back into sweaters. They’re not just to beat the fall chill — this time of year, the colors are as rich as the foliage.

There’s no doubt about it—it’s getting chillier. Even so, just because it’s cozy season doesn’t mean it’s time to pack up the one-pieces and bikinis until next summer. In fact, colder weather is one ...