Human color vision depends on three types of cone cells in the retina. Although all three contain the same light-absorbing molecule, 11-cis-retinal, differences in the surrounding protein determine sensitivity to red, green, or blue light. Understanding how these subtle protein differences produce such precise color discrimination has been difficult because cone pigments are highly unstable and structurally challenging to study.

Now, researchers led by Associate Professor Kota Katayama from Nagoya Institute of Technology, Japan, have examined red and green cone pigments from the crab-eating macaque (Macaca fascicularis), whose color vision system closely resembles that of humans, and found that just three amino acid substitutions account for nearly the entire 30 nm difference in light absorption between the two pigments.

The research team included Massimo Olivucci from the University of Siena and Bowling Green State University, Hideaki Kato from The University of Tokyo, and Hideki Kandori from Nagoya Institute of Technology. This study was published in Science in Volume 392, Issue 6,805 on June 25, 2026.