About the only thing you can count on now is that green or green/yellow is earth, and I'm not even sure I'd trust to that anymore.
I never did... it's far too easy to use 3x1.5 cable for wiring a three way switch... just tape the gn/ye... or just leave as is...
Black is a historic thing. Germany always used to have a black #1 phase, whereas Austria had cables with brown # 1 phase. For conduit wiring mostly black was used all around, and that's what I learned, so given the chance I still use black.
White, orange and purple are extensively used for stuff like switched phases, travellers ect. here whereever conduit is used. For example, a stairway lighting circuit: black phase, brown switched phase from timer relay to fixtures and purple wire from push buttons to relay. Blue neutral and ye/gn ground.
Our old system only has three wires, all colors evenly spread, changing from floor to floor (the wiring between the floors is old cloth covered wiring and on each floor they put in some old black-grey-red cable at some point)... no ground of course.