Abstracts: Brilliant animal colors are often produced from light interacting with intricate nanomorphologies present in biological materials such as butterfly wing scales. Surveys across widely divergent butterfly species have identified multiple mechanisms of structural color production, however, little is known how these colors evolved. Here, we examine how closely-related species and populations of Bicyclus butterflies have evolved violet structural color from brownpigmented ancestors. We used artificial selection on a lab model butterfly, B. anynana, to evolve violet scales from brown scales, and compared the mechanism of violet color production with that of two other Bicyclus species: B. sambulos and B. medontias, which have independently evolved violet/blue scales via natural selection. The UV reflection peak of B. anynana brown scales shifted to violet frequency over six generations of artificial selection (i.e. less than a year) due to changes in the dimensions of the lower lamina in ground scales and loss of pigmentation. These changes mimicked the natural evolution of violet/blue structural color in the other Bicyclus species, except changes sometimes occurred in a different scale type. This work shows that populations harbor large amounts of standing genetic variation that can lead to rapid evolution of scales’ structural color via slight modifications to their physical dimensions.