Comment by yxhuvud

There is nothing obvious around that - it is driven by what abstractions the language provides related to concurrency, and with different choices you will end needing different ways to interact with it.

So yes, given how the language designers of C# and JavaScript choose to implement concurrency and the APIs around that, then coloring is necessary. But it is very much implementation driven and implementation of other concurrency models then other ways to do it that don't involve keywords can make sense. So when people complain about function coloring, they are complaining about the choice of concurrency model that a language uses.