A project that I am planning is an automated glockenspiel (xylophone) that uses a serial controller and a bunch of soleniods to bang out the notes. The instrument has 37 notes and the shift registers in the circuit have 8 channels each making 5x8 = 40 channels, 40-37 = 3 left over. So I was thinking of what to do with the other three channels. I thought, why not add light to the project and include a channel for R, G, and B leds. The circuit only controls on/off via transitors without dimming, which seemed a bit boring to me. I'm not asking for a detailed schematic or long lecture on LED physics, but what are some ways I can control the intensity of each LED so I can get more colors? I have a few piezo pickups that I got really cheap. One idea I had was to use the audio signal to modulate the LED intensity, but don't know where to start there. I don't know much about LEDs, but I can figure it out. Any other cool suggestions are welcome.