Color vision, or the ability to discriminate between different wavelengths of light, is uniquely variable across primates compared with other Mammal Orders. Substantial research has focused on identifying the extent of variation in primate opsin genes, which control color vision ability. Although several primates retain the ancestral mammalian complement of a short-wavelength-sensitive (SWS1) opsin gene and medium-/long-wavelength-sensitive (LWS) opsin gene and dichromatic color vision, the Primate Order has experienced multiple episodes of gene duplication, evolution of allelic variation, and loss of gene function throughout its evolutionary history. A major area of current research is focused on using a variety of approaches to explore ecological factors influencing the evolution of primate opsin gene variation.