It probably works similar to the way the CRT or LCD on your computer works. IE, three individual color channels are modulated to make the appearance of colors.

Now if you had R G & B channels like a CRT, your on your way.

You mentioned the equipment you looked at was turning the LEDs fully on and off. It is possible that the color information is produced by PWM control to the LEDs to change the apparent intensity.

Michael Karas