(To set the tone clearly - this seems like an area where you know a _lot_ more than me, so any questions or "challenges" below should be considered as "I am probably misunderstanding this thing - if you have the time and inclination, I'd really appreciate an explanation of what I'm missing" rather than "you are wrong and I am right")
I don't know if you're intentionally using "colour" to reference https://journal.stuffwithstuff.com/2015/02/01/what-color-is-... ? Cooperative multitasking (which I'd never heard of before) seems from its Wikipedia page to be primarily concerned with Operating System-level operations, whereas that article deals with programming language-level design. Or perhaps they are not distinct from one another in your perspective?
I ask because I've found `async/await` to just be an irritating overhead; a hoop you need to jump through in order to achieve what you clearly wanted to do all along. You write (pseudocode) `var foo = myFunction()`, and (depending on your language of choice) you either get a compilation or a runtime error reminding you that what you really meant was `var foo = await myFunction()`. By contrast, a design where every function is synchronous (which, I'd guess, more closely matches most people intuition) can implement async behaviour when (rarely) desired by explicitly passing function invocations to an Executor (e.g. https://www.digitalocean.com/community/tutorials/how-to-use-...). I'd be curious to hear what advantages I'm missing out on! Is it that async behaviour is desired more-often in other problem areas I don't work in, or that there's some efficiency provided by async/await that Executors cannot provide, or something else?