rgb led won't fade correctly ..help (SOLVED)

hi

hoping to pick someone's brain to help me understand where i am going wrong. I have a few RGB led's (common Cathode) that i want to control via an arduino but with an external power supply. The LED's in question are these

http://www.ebay.co.uk/itm/290946336848?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649 wired up with 330R 0.5W resistors (I want to run this at 12v)

I have been using the schematic kindly put together by a different arduino forums user:

Using some of these PNP transistors I had lying around: http://www.onsemi.com/pub_link/Collateral/BC556B-D.PDF but when i wire it up the led does not fade all the way to black.. I am a bit confused as to what the fault is, my first guess is the PNP transistor, but could someone advise me what would be a more suitable one for my application?

am i also correct in my understanding that i need to have a common ground between the arduino GND and the power supply?

Try this hook up on one led.

thanks larry - problem solved!