A "Red Box" was one of several 1900's Phone Phreaking Color Boxes, which was basically a tape loop of the sound that Pay Phones made when you put coins in them. It fooled the phone company into registering the coins so that free calls could be made. Although the telephone network may still work with Rotary Phones, it has evolved away from the simplicity that permitted such simply bizarre tinkering. The colors must have been arbitrary since standard color coding for cracking tools would have only been beneficial to Law Enforcement. It is also probably unreasonable to assume that the law anticipated simple unintended ambiguities being exploited in the system.