[dwohnitmok]

That's kind of not a language-level thing. I mean it is, but it's tied very very closely to runtime choices rather than the language itself.

Basically your question is equivalent to asking whether the language has green threads. The original article describing color (http://journal.stuffwithstuff.com/2015/02/01/what-color-is-y...) says it's just threads, but it glosses over why a language like C# decided to add async-await and why Java now has its ongoing Loom project.

System threads are heavyweight and as a result usually unsuitable as your concurrency primitive for highly concurrent applications (although you can and most runtimes do build on top of threads). And so if you only have that, you inevitably get what the article calls the "color problem" (see e.g. in Java the async IO APIs, which the article laments, but doesn't explore why they exist and moreover are often preferred by Java programmers over their synchronous equivalents), because system threads aren't enough and a color-based solution inevitably must appear on top of them.

So the question to ask is "does Nim have green threads?" To which the answer is no (and then by extension it does have the color problem, in this case via async-await).