What do the different colors on household electical wiring signify?

In the United States, household electrical wiring typically uses one black and one red conductor to distinguish the ungrounded or hot conductors. This serves no purpose other than to be able to identify one wire from the other at each end. In any singe phase system, such as a home, on a 220v circuit, it matters not what position each conductor is terminated. On branch circuits, black is generally used on all 110v circuits, and a combination of black and red are used on all 220v circuits.

White is used to identify the grounded or neutral conductor. And the green or bare conductor is used for the equipment grounding conductor, commonly called "the ground."