While the word 綠 to mean green has been attested as far back as 1000 BC, the idea that it was a separate color rather than describing a shade of 青 is relatively more recent. Wikipedia[0] indicates that it was adopted in the early 20th century in Chinese (as part of vernacular language reforms) and after WWII in Japanese, though these claims are currently marked with [citation needed]. While both are relatively recent, the usage in Chinese did have a longer period of time to take hold.

[0] https://en.wikipedia.org/wiki/Blue%E2%80%93green_distinction...

By the way there’s a variety of kanji that reads “aoi” in modern Japanese. 青い, 蒼い, 碧い are all “aoi”, but we use 青い mainly as blue today.

EDIT: I apologize for the vague sourcing!