A quirk of human vision. Our "red" cone receptors in our retinas are mostly sensitive to redder hues, but also have a bit of a bump down in the violet part of

A quirk of human vision. Our "red" cone receptors in our retinas are mostly sensitive to redder hues, but also have a bit of a bump down in the violet part of the spectrum. This shows some graphs that sort of explain it: https://physics.stackexchange.com/questions/433119/why-does-purple-appear-in-a-rainbow https://physics.stackexchange.com/questions/433119/why-does-... However, such spectral sensitivity graphs vary a lot (perhaps because people's vision does, but also they'll be measuring things differently): https://duckduckgo.com/?q=retina+cone+frequency+response&atb=v279-1__&iar=images&iax=images&ia=images https://duckduckgo.com/?q=retina+cone+frequency+response&atb...