A phreaking box is a device used by phone phreaks to perform various functions normally reserved for operators and other telephone company employees.
However, very few physical specimens of phreaking boxes are actually the color for which they are named.
Most phreaking boxes are electronic devices which interface directly with a telephone line and manipulate the line or the greater system in some way through either by generating audible tones that invoke switching functions (for example, a blue box), or by manipulating the electrical characteristics of the line to disrupt normal line function (for example, a black box).
Many text files online describe various "boxes" in a long list of colors, some of which are fictional (parodies or concepts which never worked), minor variants of boxes already listed or aftermarket versions of features (line in use indicators, 'hold' and 'conference' buttons) commonly included in standard multi-line phones.
This list of boxes does not include wiretapping "bugs", pirate broadcasting apparatus or exploits involving computer security.