Video of it working:
Step 1: Materials
* Red LED
* Green LED
* Blue LED
* RGB LED
* 3 phototransistors - I used OP550B's, but others could be used.
* 6 220 ohm resistors
* 3 10k ohm resistors
* Cardboard or some other divider to separate the LED's
* Breadboard or circuit board and soldering materials
* Arduino and usb cord
* Electrical tape
* Cards of various colors - I used index cards covered in electrical tape of different colors.
Step 2: Step 1: Create the Circuit Board
* Make sure to leave enough room to superimpose the dividers - in my case a compartmentalized cardboard box - later.