Colour Strike
At the time, ITV had recently switched to transmitting programs in color. This needed new equipment. The cameras had four tubes: three were for the color information (Red, Green and Blue) and one for the black and white information (called luminance). The black and white information was need as most houses didn't have sets to show a color picture. The striking technicians turned off the color tubes causing the cameras to only pick up the black and white signal and therefore causing the programs to be recorded in black and white.