Guess I am more soul then techno.
I know it was not plugged into a computer because we did not have them yet in the private sector. Mine was made by this guy who does the kinds of work you discribe, the electronics would compute what sound would trigger what colored light. If you do a math problem you are computing something. The radio shack cheapo thing came out later on and was stupid because they did not even have knowledge about which colors should be computed to go with which music tones. Totally un-Zen of them.
The model I have (hand made) would also illuinate stronger if the music was louder, but keep the same colors when the volume was turned down, but the light would be dimmer. They have simular color patterns now used for screen savors or at websites where you download music, but not in conformity with the music.
Most of the hand made hippy light shows were made with TV sets where they used the TV tube for the screen. It was in my opinion one reason why they also came up with the ideas for TV like screens that are used to display what ever effect is plugged into the monitor, from a typewriter like keyboard to stereo like hard drives and software. They also wire it together in part with "cheap radio shack wiring" - which might not be that cheap cost wise, come to think of it. There are common principles involved and related ideas. Of course a ship would not use a Bat's Ear for it's radar receptor, but the idea is the same.
Here is the "how things work" webpage I use.
http://www.deoxy.org/8brains.htm
Cheers,
Technosoul.