Red, Yellow, Green
I've been using Mac OS X for several months now, and it just dawned on me. You know the red, yellow and green colors used for the close, minimize and zoom buttons? They look like this:
Sure, those colors may be commonly associated with "stop", "slow" and "go". But I think they were picked because they're the colors for the common apples-- red, yellow and green.
Okay, maybe not. But you never know.