The diverse color patterns that decorate the wings of butterflies and moths are products of evolutionary selection. Wing patterns are formed by the spatially ordered scales produced by stem cells in the developing wing in the pupa. The stem cells are monochromatic, so that each scale contains a single color pigment. The colored scales are the unit basis of color patterns, and were a key innovation in early lepidopteran evolution. The spectacular complexity of the color patterns is illustrated here by a detail of the wing of a Silver Y moth.