You seem to raise valid points and I don't disagree with you, however I don't see how it's relevant to the original concern regarding colored functions.
I suppose I'm struggling to understand what "colour" means in the context of Rust. It's surely just another word for signature. For some reason it's trotted out every time there's a discussion about async. I can only assume it's to do with the original use of the term for JavaScript async (which I know almost nothing about and have no opinion on), but I just cannot see its point in Rust async.
It has to do with the fact that most of the code in the project is not async but having to call async functions often propagates all the way to your main function. It's infectious and many people don't like it, myself included, that's why I'm working with Elixir and Golang where async is transparent and 99% automatic, or explicit but non-infectious, respectively.
I do love Rust and found a number of very valid uses for it but its async story leaves a lot to be desired. I don't enjoy writing it though I do enjoy the results.
