Many New World (NW) primates possess a remarkable polymorphism in an X‐linked locus, which encodes for the visual pigments (opsins) used for colour vision. Females that are heterozygous for opsin alleles of different spectral sensitivity at this locus have trichromatic colour vision, whereas homozygous females and males are dichromatic, with poor colour discrimination in the red–green range. Here we describe an extensive surve...