The LEDs need a resistor to get the voltage down to an acceptable level, and it does not matter if the resistor is on the anode side or if its on the cathode side, as long as it is in series with the LED right?
Then why are there 3x 220 Ohm resistors between the RGB LED and Digital PWM pins 9,10 and 11. Could there not just be 1 instead? between the cathode and ground? Would that not have the exact same effect?