Colour-Vision Deficiency in old-world primates: A case study

The monkey is clearly a dichromat, unable to distinguish reds and greens, which is why his painting is dominated by the tonality of blues and yellows which stand out from grey for him.

One would take this for granted if he were a New World monkey of the Platyrrhine clade, where dichromacy is the norm (apart from Howler monkeys who evolved trichromacy independently, and heterozygous females in many New World genera). But in fact he is a Catarrhine, a Macaque of one species or another, where trichromacy is the norm.

For some reason all the research on colour-blindess in old-world primates has concentrated on humans.