Colored functions are good. It reflects the language design on signaling what is important, and what are the properties it want the writer to pay attention.
Other examples of colored functions:
* Haskell: pure function and non-pure (IO monads) looks different.
* Rust: unsafe functions (or block) requires special markers.
* Haskell: pure function and non-pure (IO monads) looks different. * Rust: unsafe functions (or block) requires special markers.