International DC wiring color codes call for greenish-yellow ground wires, brown positive wires and gray negative wires. Blue wires are used for the mid-wires in a three-wire grounded circuit.
The International Electrotechnical Commission sets the wiring coloring codes for most of Europe, including the United Kingdom. For the most part, DC wiring follows the color codes established for AC wiring. The United States uses its own color codes for AC and DC wiring. For DC wiring, the protective ground wire is green or greenish-yellow, negative wires are black, positive wires are red, and white wires are used as the mid-wires in a three-wire grounded circuit.