Predictors of male monarch butterfly mating success have eluded researchers for years. Although it has long been known that there is variation in male mating success in this species, the source of this variation remains unclear. We used digital image analysis techniques to measure fine-scale variation in three components of the orange color (hue, saturation and brightness of the orange) of the forewings of 174 males at a level of detail that has not been possible until recently, and we compared this information to the mating success of the males in captivity. A second experiment involved addition of orange coloration to the wings of 93 males before mating trials. Our results indicate that one component of the orange color (saturation) correlated with mating success in our first experiment. Furthermore, wing color manipulations had no effect, but the original saturation values of the males in the second experiment were directly related to mating success. Our results provide the first evidence that wing color in monarch butterflies relates to mating success, and they serve as an important starting point for future research.