[joshsegall]

Author here. You're right in the sense that some forms of function coloring have good tradeoffs, though I think that's a watered down version of that original meaning. The point is that async/await tracks the wrong thing in the wrong direction, not that "tracking effects in types is bad." In a proper effect system, subsumption goes the right way: pure is universally callable and handled effects disappear. Async/await inverts this: the "simple" color (sync) is the restricted one.