In Harvard’s Pierce Hall, the surface of a small germanium-coated gold sheet shines vividly in crimson. A centimeter to the right, where the same metallic coating is literally only about 20 atoms thicker, the surface is a dark blue, almost black. The colors form the logo of the Harvard School of Engineering and Applied Sciences (SEAS), where researchers have demonstrated a new way to customize the color of metal surfaces by exploiting a completely overlooked optical phenomenon.