The wiring (color) of the live wire differs depending on the system voltage, phase number and whether it is alternating or direct current. In common household circuits in the United States a licensed electrician would have installed a 120V AC system where the live wire is black.
A live wire is typically the wire which is not the neutral, common or ground wire. This is not to say that the live wire is the only wire needing attention as far as electrocution is concerned.
The live wire delivers current to a device and that current is returned to the source by way of the neutral wire, which is typically white. The ground wire is typically green or bare copper and is provided for protection in the case of a short circuit.
Working on live circuitry should only be attempted by a professional.