We evaluated whether dichromatic capuchin monkeys (Cebus capucinus) were more efficient than trichromatic monkeys at capturing camouflaged and non-camouflaged insects. Through fecal DNA analysis, we determined the genotypes of the M/LWS opsins for 34 capuchins in two groups inhabiting Santa Rosa National Park, Costa Rica. Dichromatic monkeys were more efficient at detecting camouflaged, surface-dwelling insects, especially under conditions of low ambient light. However, unexpectedly, trichromats were more efficient in extracting embedded, non-camouflaged, insects from substrates. To our knowledge, this is the first study to document a foraging advantage to dichromatic monkeys in the wild. Our findings show that there is a lack of heterozygote advantage in foraging for surface-dwelling insects and therefore indicate this mechanism may not be the sole driving force maintaining polymorphic colour vision in this population.