The U.S. National Electric code and Canadian Electric Code mandates only white or grey color be used for neutral wires. The International Electrotechnical Commission and countries that abide by it, such as the United Kingdom, use blue for the wiring color code for neutral wire of AC branch circuit.
Color codes for wires helps ensure easy and proper identification of the wire types and safety precautions required. A neutral wire in AC power provides a low-impedance path to earth or ground to prevent passage of heavy voltage through the equipment. A neutral wire is generally prevalent in a polyphase AC system.