Although they are called 'black boxes,' aviation recorders are actually painted bright orange. This distinct color, along with the strips of reflective tape attached to the recorders' exteriors, help investigators locate the black boxes following an accident. These are especially helpful when a plane lands in the water.
There are two "black boxes" on modern day aircraft. One is the Cockpit Voice Recorder (CVR) used to record cockpit, intercom, and pilot to controller communications. The other is the Digital Flight Data Recorder (DFDR) used to record aircraft flight control inputs, flight parameters (speed, altitude, etc.), and system performance. The primary use for both is in accident investigation.