> In Go or Rust, returning an error is also a “color” that spreads out to the top of the call stack.

That's wrong... Suppose A calls B and B returns a Result<T> (so it's colored as you say). A can match both the Some() and the Err() variants of B and return something other than the error in the latter case. So A can shed the color. There is no way to "shed" async-ness like that in javascript.