What are colored functions?
In terms of async, it's when you have to have a function with "async" attached to it and making it so that only other async functions can call async functions.
It ends up creating a weird circumstance where you can end up with a lot of duplicated APIs, particularly in libraries, because you are providing both async and non-async versions of functions.
For instance, if you resolve a future in the wrong context you'll still have problems - the coloring is just a compile time error that you are doing things wrong, rather than a runtime deadlock.
[0] https://journal.stuffwithstuff.com/2015/02/01/what-color-is-...
The terminology is used to talk about languages that have async and sync functions where you declare (or color) the function as either async or sync.
In these languages it's pretty common for the language to enforce a constraint that async functions can only call other async functions. Javascript / Typescript, Python are popular examples of languages with colored functions.
In this context: functions anotated with async