So, back in the days, there were only 4 colors names in Japanese; black, red, blue and white.

赤 (aka, red) was used for all warm colors like red, orange, yellow, and brown. 青 (ao, blue) was used all for cool colors like blue, violet, and green. Colors like yellow and green were not considered unique colors. They were encompassed in either red or blue. That means leaves and bamboo are blue!

The part I truly love is how red also meant bright, while black meant dark. White and blue were used for describing clarity. White was clear, whereas blue was vague.

Interesting read from Louie Mantia, Jr. over at his 日本語 blog; 何だっけ (nanddake): https://nandakke.jp/blog/ao.html