Aposematism is one of the great mysteries of evolutionary biology. The evolution of aposematic coloration is poorly understood, but even less understood is the evolution of polymorphism in aposematic signals. Here, we use a phylogeographic approach to investigate the evolution of color polymorphism in Dendrobates pumilio, a well-known poison-dart frog (family Dendrobatidae), which displays perhaps the most striking color variation of any aposematic species. With over a dozen color morphs, ranging from bright red to dull green, D. pumilio provides an ideal opportunity to examine the evolution of color polymorphism and evolutionary shifts to cryptic coloration in an otherwise aposematic species. We constructed a phylogenetic tree for all D. pumilio color morphs from 3051bp of mtDNA sequence data, reconstructed ancestral states using parsimony and Bayesian methods, and tested the recovered tree against constraint trees using parametric bootstrapping to determine the number of changes to each color type. We find strong evidence for nearly maximal numbers of changes in all color traits, including five independent shifts to dull dorsal coloration. Our results indicate that shifts in coloration in aposematic species may occur more regularly than predicted and that convergence in coloration may indicate that similar forces are repeatedly driving these shifts.