Very cool, and you should consider making this into a book. I recently bought a similar book of traditional Japanese color combinations: A Dictionary Of Color Combinations Vol.1 and Vol.2 with Japanese Traditional Colors Chart.

https://en.seigensha.com/books/978-4-86152-772-2/

I wonder if the colors were programmatically extracted from the photographs

In case anyone is looking, there are many tools for that, e.g.:

https://color.adobe.com/create/image

https://qtiptip.github.io/Pylette/

https://extract-colors.namide.com/

right now this is showing up below Why is the world losing color - https://www.culture-critic.com/p/why-is-the-world-losing-col... - not sure if I should consider it a counter argument, or just a funny juxtaposition.