Rust pretty much had to add function coloring, because of its low-level nature. Other languages can get away with it due to having a runtime, notably Go, and with the coming Project Loom, Java. For higher level languages, I do believe that coloring is not a useful concept, similarly to how you use a GC, instead of manual memory management. The runtime can “hijack” calls to IO or other blocking functions and can park a virtual thread, and resume execution afterwards automatically. There is no useful information in coloring in this case.