The different colors of electrical wires indicate the function of the wire, with black and red indicating the wires carry electric current, white usually indicating neutral charge and green indicating the wire is grounded. The colors, regulated by the National Electrical Code in the United States, are standardized for safety.
Black wires are always hot wires, meaning that they carry electricity. Black wires are never used as ground or neutral wires and must always be treated with caution. Red wires are also hot wires. As hot wires can be connected to each other, a black wire can be connected to a red wire. White wires are always neutral in 110-volt circuits but can be used as the second hot wire or switch leg in 240-volt applications and three-way switches, respectively. Green wires are used for grounding and should only be connected to other green wires.