The hindquarter and facial coloration don’t accurately propose the timing of the primates fertility phase, while the hindquarters luminance variation indicated differences between the different ovulation stages.

The faces became lighter while the hindquarters turned less red as the successive cycles increased. The hindquarters of these primates became redder during non-conceptive cycles as compared to conceptive ones.

In good lighting, the skin luminance and redness appear perceptible. Darker hindquarters can be seen on top-ranking females. Also, the study found that color variations might contain information relating to body mass differences but not in parity.

The female Japanese macaques’ coloration might be indicative of specific female characteristics and inter-cycle variation rather than their fertile phase.