The color organ of my era was a wood box about the size of a medium size bookshelf speaker, that had colored lights in it (mine had red, green & blue lights). The box also had some sort of diffusing plastic on the front and some circuitry inside that listened for; and separated the 3 levels of sound (bass, midrange & treble) in the music or other sounds. The idea was that when playing music on your stereo, the color organ would sense the sound and the lights would in turn flash to the beat of the music and the color would change based on the bass, midrange or treble content in the music. For instance, during quieter passages, the green and blue lights would flash calmly off and on, but as the music got louder with more intense bass, the lights would turn more red. This was the best thing since sliced bread!
The color organ that I purchased back in the 1970s, was a do it yourself kit from Radio Shack in Glendale, California (see video link below for a similar color organ to mine). The kit came with a walnut finished box, ok, it was actually simulated wood grain vinyl laminate over particle board, all the electronic components and light bulbs. The box also included a sheet of prism plastic which enclosed the front of the box.
The kit was fairly straightforward to put together, you assemble the electronic components on the printed circuit board and solder them in place, you install the lamp sockets, wire them to the circuit board and screw in the bulbs and test. This particular color organ used a microphone built onto the circuit board to sense the audio levels being played around it as apposed to a hard wired circuit to your stereo. To test, you play some music on your stereo, and adjust the potentiometers on the circuit board to balance the amount of sensitivity between the three different flashing colored bulbs. So cool!
The color organ is still around today and can be found in abundance on the web for very reasonable prices. If you decide to get one of these, HAVE FUN!!!
More details at Wikipedia.com:
This guy has the same brand of color organ that I had.