With electrical conductors marking and colors have meanings.
Electrical wires will have markings stamped or printed on the outside covering of the cable. These markings will tell what type (NM, SO, THHN, TWN etc…) and size of wire that you have.
But another aspect is color, the color of the wires inside of the sheath, like in type NM cable, will reveal that different color wires serve different purposes.
Black/Red wires are always used for hot/line wires (conductors). (Note: other colors (other than white/grey/green) can used for hot/line conductors in various other applications such as 3 phase, cable trays/raceways and controllers)
Green or green yellow wires and bare copper wires are used only for grounding wires (conductors).
White or Grey is used for neutrals( grounded conductors) wires.
(In wiring a switch or 240v circuit the electrician may use the white wire as a second hot conductor but needs to be re-identified/marked at each end of the wire with black (electrical tape or permanent marker).
For conductors larger than #6 you can identify an EGC that is not green by painting or covering the exposed insulation green, removing the exposed insulation, or marking the insulation with green tape or labels. Note however that the prohibition on using white or gray for anything other than a grounded conductor still applies so you cannot re-identify a white or gray conductor for use as an EGC.