Actually, the black box is day-glo orange. And there are two of them.
The first is the Cockpit Voice Recorder. It records not just what is said in the cockpit, but also all the background mechanical sounds that provide clues to determining the chain of events leading to the accident. The NTSB, along with other parties to the investigation, listens to the CVR, and then prepares a transcript of what it hears. The transcript, or parts of the transcript, may be released to the public. The actual recording, however, is almost never made public, mainly out of concerns over the crew’s right to privacy.
After an accident, we will often hear on the news the crew’s conversation with Air Traffic Control. Sometimes the news media report that the recordings are the "cockpit tapes." They’re not. What we are hearing is the recording made by Air Traffic Control. So we are hearing only what the crew decided to transmit over the aircraft’s radio. We’re not hearing what the crew said amongst themselves. Those discussions are on the CVR only.
The second "black box" is the Flight Data Recorder. That box records things like the aircraft’s heading, altitude, airspeed, and position of the aircraft’s flight controls. The information from the Flight Data Recorder frequently allows the NTSB to reconstruct the flight all the way up to the moment of impact.