The three colors used in most home electrical wiring are blue, yellow and red, notes AllAboutCircuits.com. Air conditioning wiring in the United States also uses green, white and black wires.
In the United States, neutral power conductors must use the colors white or gray. Protective ground wires must be either green, green with a yellow stripe or bare copper, and, in most cases, any other wire color may be used for power conductors. Generally, red, blue and black are used for 208 VAC and brown, orange and yellow for 480 VAC.
Line, three-phase wires are labeled L1 and are black or brown. Line, three-phase wires labeled L2 are red or orange and L3 wires are blue or yellow. Neutral wires are white or gray.
The wiring for power circuits is more complex but generally follows the same color scheme. In a power circuit, negative wires labeled L- are black and positive wires with the L+ label are red. The mid-wire, labeled N, is white. These color codes are applicable in a three-wire grounded DC circuit.
In a two-wire grounded DC power system, the positive of a negative grounded circuit wire is red and marked with the L+ symbol. The negative of a negative grounded circuit, marked with an N, is white. The wire for the negative of a positive grounded circuit is black and labeled with an L-.