What color is the hot wire on a 120 volt circuit?

Black typically. Red possible. White is neutral.

White could be a hot in 220 V circuits, but it should be taped red or black.

Much of this depends because 2 conductor NM-B cables with ground are black white and bare.
3 conductor with ground are black, white, red and bare.

Switches are wired with 2 conductor cable and switch the hot lead, so one of the hots is white. That white should be taped black.

With a 4 wire system with L1(black), L2(Red), N(White) and ground, Red to White is 120 V and so is black to white.