What is the genetic architecture of morphological evolution? Is there uniform potential for novelty across a genome or, on the contrary, can a small number of large-effect genes explain the phenotypic variation observed within and between species? Here we highlight recent work on butterfly wing pattern genetics showing that a small set of loci can be repeatedly involved in the evolution of complex traits. These loci behave as genomic hotspots for diversification because they underlie adaptive variation within and between species with both convergent and highly divergent wing patterns. These findings suggest that certain loci may be more likely than others to facilitate rapid evolutionary change.