Why so convoluted?Just drive with 3 logic level, low Rds, low Gate capacitance, N-channel MOSFETshttp://www.digikey.com/product-detail/en/NTD5867NL-1G/NTD5867NL-1GOS-ND/240142210k pulldown resistor to hold gate off while arduino starts up.
I think this is the way to go, as someone in another forum told me:
Ok, the led is this one: http://www.alibaba.com/product-gs/712130845/10_Watt_RGB_LED_high_power.html
That will work better using a voltage regulator for the Red.Can you snip off the top of the device so you have seperate anodes for the 3 LEDs?Then you can have 12V for Green & Blue, and regulated 8V for the Red, and the cathodes can connect to your circuit above.
I would switch to a forum where they didn't tell you such rubbish.For a start that is not a proper circuit and second you always need one resistor per LED.