In my brick & mortar houses, I've always had two wires, (black or red or other colors) and white. White eventually finds it's way into the ground via a water pipe or similar. Colored wire including black goes to the breaker box. It is common for odd colors to represent temporary on, for example between light switch and ceiling fixture.
The 3rd round prong gets grounded via metal junction box & conduit. Unlike much of the USA, we are not allowed to use open rubber-coated Romex wiring, I believe to protect the wiring from rodents....a long-ago Chicago-originated requirement.