Baird was an early pioneer in this area, and one of the first techniques developed employed a system whereby the normal frame frequency was increased by a factor of three, each successive frame containing the material for one primary color. The receiver used revolving color discs in front of the viewing screen, synchronized with the correct frame colors at the camera. A similar system replaced the color discs by three superimposed projected pictures corresponding to the three primary colors. Baird demonstrated color TV in London in 1928, but it was not until December 1953 that the first successful system was adopted for broadcasting, in the United States. This was called the NTSC system, since it was developed by the National Television System Committee, and variations of it have been developed in Europe; for example, SECAM (sequential and memory) in France and Eastern Europe, and PAL (phase alternation by line) in most of Western Europe. The three differ only in the way color signals are prepared for transmission, the scanning rate, and the number of lines used. When there was no agreement on a universal European system in 1964, in 1967 the UK, West Germany, the Netherlands, and Switzerland adopted PAL while France and the USSR adopted SECAM. In 1989 the European Community (now the European Union) agreed to harmonize TV channels from 1991, allowing any station to show programs anywhere in the EC.
The method of color reproduction is related to that used in color photography and printing. It uses the principle that any colors can be made by mixing the primary colors red, green, and blue in appropriate proportions. (This is different from the mixing of paints, where the primary colors are red, yellow, and blue.) In color television the receiver reproduces only three basic colors: red, green, and blue. The effect of yellow, for example, is reproduced by combining equal amounts of red and green light, while white is formed by a mixture of all three basic colors.
Signals indicate the amounts of red, green, and blue light to be generated at the receiver. To transmit each of these three signals in the same way as the single brightness signal in black-and-white television would need three times the normal band width and reduce the number of possible stations and programs to one-third of that possible with monochrome television. The three signals are therefore coded into one complex signal, which is transmitted as a more or less normal black-and-white signal and produces a satisfactory