This "lens brunescence" theory is very odd and likely wrong: lens yellowing does not impact the ability to distinguish blue from green under even modest illumin

This "lens brunescence" theory is very odd and likely wrong: lens yellowing does not impact the ability to distinguish blue from green under even modest illumination levels. While it's a substantial effect by age 90 [1], it would be also be strange to assume that 90 year olds are responsible for all of language. In mammals, the primary opponent color channel is along the B-Y axis (comparisons between the S-cone to the M-cone), so many mammals are dichromats, and tritanopia is quite rare. Color adaptation is also quite effective along this axis, which means people adapt to changes in yellow vs. blue quite readily, seeing a wide range of colors as "white". Here's an alternate hypothesis: more daylight gives more days with a "blue sky" (instead of an overcast one), and so people in sunny climates would be much more likely to need a word to describe what they see. 1. For lens yellowing, see https://people.brandeis.edu/~sekuler/SensoryProcessesMaterial/eyesGetOld.html https://people.brandeis.edu/~sekuler/SensoryProcessesMateria... for an illustration.