When you look at an RCA or RGB connector, there are a variety of color codings on them. For each color there is a corresponding audio or video signal or format. In the back of all consumer electronics products there are matching color codings. This enables the consumer or professional who is doing the installation to use the color codings and greatly simplify the hook up.
An RCA jack, also called a phono jack, is one type of electrical connector that may be commonly used in the audio / video market. It is used for composite video and stereo audio. The name of the connector, RCA, comes from the Radio Corporation of America. This is the company that introduced the design in the early 1940's to enable phonograph players to be hooked up to amplifiers. The RCA connector began to replace older jack plugs for many other applications when component high fidelity became popular in the 1950's. The plug connector that corresponds to an RCA jack is an RCA plug.
The RCA connector has been adopted for numerous uses other than the original intention, including power connector, RF connector, and loudspeaker cable connector. It is also commonly used for composite video signals as well, but this application gives very bad impedance matching. RCA connectors may also frequently be used to carry SPDIF-formatted digital audio, with these plugs orange colored to distinguish them from any other typical connections.