The common buckeye, Junonia coenia (Hübner), is a North American nymphalid that shows seasonal wing color plasticity. Throughout much of its range the ventral hindwings are tan in the spring and summer and dark red in autumn. Although this species has long been used as a model to study the physiology and genetics of plasticity, the function of its seasonal color variation is still largely unknown. Here we investigate the effect of buckeye wing color on wing and body temperature and ask to what extent seasonal plasticity is associated with behavioral differences. By using real time infrared imaging of different seasonal morphs from a laboratory colony of North Carolina J. coenia, we observed that red autumnal butterflies warm up faster and reach higher final temperatures than tan summer butterflies. Furthermore, behavioral trials at field sites revealed that red butterflies are less physically active than tan butterflies. Based on our findings, we propose that the dark red wing coloration of autumn morphs could be useful for helping individuals reach higher body temperatures faster while basking on colder days. We also speculate that lower activity levels of autumnal butterflies may help conserve energy.