Rust unsafe functions aren't a good example of colored functions because it doesn't exhibit the main issue brought up in the article, that one color can call the other but not the other way around.

In Rust, unsafe code can call safe code, and safe code can call unsafe code. Calling unsafe code in safe code requires an explicit unsafe block, but that's fairly normal and not a hack to get around function coloring.

A better example could be Rust async, though unlike JavaScript, you have the option to block the thread on an async function in a sync function.

My mind went to Java's checked exceptions -- not sure if anyone today believes that coloring is still a good idea.