this is what i was told once: on adafruit forum
Starting with discrete RGB leds, you are looking at 100 RGB leds, 300 resistors, and 300 I/O pins to drive them. The leds and resistors are straightforward enough. 300 I/O pins is a little more involved. The Arduino has 20. The Mega still only 69. You will need some port expanders like the MCP23017. You can chain up to 8 of these on an i2c bus for 128 pins. Using 'softI2C, you can create multiple i@c busses to get beyond that.
There is no easy answer to your question
i don't know if they think everyone knows as much as they do or what.