I think Java does have coloured functions. It's just that the colours are "fast" and "slow" - i.e. functions which will block the thread for a long time and tho

I think Java does have coloured functions. It's just that the colours are "fast" and "slow" - i.e. functions which will block the thread for a long time and those which don't. You can't call "functions that may block for a long time" from a UI thread. Java doesn't have async, so you have to punt them to a background thread manually.