Several systems of color television have been developed. In the first color system approved by the Federal Communications Commission (FCC), a motor-driven disk with segments in three primary colors—red, blue, and green—rotated behind the camera lens, filtering the light from the subject so that the colors could pass through in succession. The receiving unit of this system formed monochrome (black-and-white) images through the usual cathode-ray tube, but a color wheel, identical with that affixed to the camera and synchronized with it, transformed the images back to their original appearance. This method is said to be "field-sequential" because the monochrome image is "painted" first in one color, then another, and finally in the third, in rapid enough succession so that the individual colors are blended by the retentive capacities of the eye, giving the viewer the impression of a full colored image. This system, developed by the Columbia Broadcasting System (CBS), was established in 1950 as standard for the United States by the FCC. However, it was not "compatible," i.e., from the same signal a good picture could not be obtained on standard black-and-white sets, so it found scant public acceptance.
Another system, a simultaneous compatible system, was developed by the Radio Corporation of America (RCA). In 1953 the FCC reversed its 1950 ruling and revised the standards for acceptable color television systems. The RCA system met the new standards (the CBS system did not) and was well received by the public. This system is based on an "element-sequential" system. Light from the subject is broken up into its three color components, which are simultaneously scanned by three pickups. However, the signals corresponding to the red, green, and blue portions of the scanned elements are combined electronically so that the required 4.1-MHz bandwidth can be used. In the receiver the three color signals are separated for display. The elements, or dots, on the picture tube screen are each subdivided into areas of red, green, and blue phosphor. Beams from three electron guns, modulated by the three color signals, scan the elements together in such a way that the beam from the gun using a given color signal strikes the phosphor of the same color. Provision is made electronically for forming proper gray tones in black-and-white receivers. The FCC allowed stereo audio for television in 1984.