A major focus of behavioral ecology is to understand the evolutionary causes and consequences of sexual signaling. Great strides have been made, particularly in the realm of color-based signaling, using model organisms in target groups such as birds and fish. Such work has demonstrated how information regarding phenotypic and/or genetic quality may be encoded in various types of color ornaments, which thereby offers an explanation to their adaptive value in mate assessment. However, until recently, attempts to examine such hypotheses have rarely used butterflies as subjects. This is surprising on several fronts. First, butterflies display an exceptional diversity of coloration, which is generated by a large breadth of color-production mechanisms and which provided part of the impetus for Darwin's ideas about sexual selection. Second, butterflies are well suited to behavioral, physiological, morphological, and genetic investigations, and features of their life history make them a novel venue for testing ideas about the potential information value of color signals.In this chapter, we review how studies of butterflies have advanced the field of color signal evolution. Lepidopteran wing coloration has long (and sometimes famously) featured in studies of behavior, genetics, and evolution; our focus here is on efforts to understand the evolutionary ecology of highly exaggerated and male-limited wing markings. Behavioral experiments have revealed female mating preferences for male coloration that transcend simple species and/or mate recognition. These findings have, in turn, promoted butterflies as a system for testing and refining theories of mate-quality signaling, including models based on the signaling of genetic quality. Coupled with this, physicists have seized upon butterflies as a vehicle for understanding natural photonic structures, thereby unearthing an impressive array of color mechanisms (such as three-dimensional crystalline structures) and fuelling the further refinement of signaling hypotheses. We review this progress, showcasing work in the two Coliadine genera Colias and Eurema and focusing on the relevance of this work to our understanding of signaling system evolution.