When I taught high-school electronics in the 1970s, one of the projects I had students build was a "color organ".
This used any audio signal to drive a small simple amplifier circuit connected to a simple filter network (very similar to the crossover network of a 3-way speaker system).
There were three outputs; Low, Midrange, and High and these in turn drove Triacs which modulated 3 sets of colored lights (7 watt Christmas tree lights).
One color was modulated by the high-frequency content of the audio, one by the midrange, and one by the bass. Any color of lights could be chosen for each output.
This was a great educational project, because it taught amplifier principles, frequency division (filtering), power control (triac operation), and they had a fun "psychedelic" gizmo to modulate lights that responded to their music (just the thing for getting stoned...lol).
They usually built a cabinet with a diffuser panel to put the lights in to create various effects from the lights.
This type of color organ circuit (not counting the lights and cabinet) can be built for around $25 in parts (it was a lot cheaper in 1975).
Amazon has several commercially packaged color organ kits available for either 12V lights or 120V AC lights. These cost around twice as much as doing it yourself from scratch.
Just go to Amazon and search for "color organ".
