Using one color to enhance a slender illusion is the oldest trick in the book, and for a good reason: It helps create a long vertical line. While wearing head-to-toe black is the most effective—and eternally chicest—option, other darker hues work well too, such as navy, oxblood, and green. The trick to monochrome dressing: Keep each silhouette crisp and tailored, and stay away from pale shades like beige.