MarkT:
You might be interested to know you can now get RGB LEDs in strip form complete with driver chips that allow individual control via some sort of serial interface to every LED - not cheap, but then 32 RGB leds aren't that cheap anyway - looks interesting and might be
useful for this project:RGB LED Strip - 32 LED/m Addressable - 1m - COM-10312 - SparkFun Electronics
And as a bonus, Sparkfun has supplied a example code! I am already getting this for light painting.