I am an enormous fan of the unambiguous UI design adopted in aircraft cockpit displays.
Only six colours are used for text:
White - Used for UI labels and other fixed values.
Green - Values provided by the crew (e.g. text input.)
Cyan - Values provided by the aircraft (e.g. sensor readings.)
Amber - Things you need to be aware of and keep an eye on that could be a problem.
Red - Things that are an immediate danger to your safety.
Magenta - For navigation purposes, where you should be aiming the aircraft.
On touch screen UIs, buttons are bevelled grey and so what you can touch and what you can’t is extremely obvious.
Activated buttons are a distinctive colour. This colour varies between vendors but at least it’s consistent for a particular aircraft type; usually a light blue on Airbus, green on Boeing. The green seems most consistent with the text colour system, the button is green because the crew pressed it.