Is there a color requirement for the selection of phase line and center line?

Three-phase, four-wire and five-wire can all use one color (specification)

Where the three-phase four-wire system is adopted, the phase line is yellow-green-red, and the zero line is blue or black (specification).

Where the three-phase five-wire system is adopted, the phase line is yellow-green-red, the zero line is blue, and the grounding line is black (specification).

Single-phase incoming wire three-wire system, phase wire yellow, green and red, zero wire blue, ground wire yellow, green and double color (specifications).

Single-phase household two-wire system, with yellow, green and red phase wires and blue or black zero wires (specifications).

In any case, the two-color line can only be grounded.