Guys and Girls,
Having at last sourced a sat nav head unit with colour screen that fully functions (except cd player - doh), I can confirm that a colour screen does not need to be 'paired' with the head unit. The head unit needs to be paired with the ECU - so will need to be placed in delivery mode while in the donor car before removal. Only then can it be programmed into a new car; that new car will need the car pass with radio/immoboliser codes for Tech2.
I initially purchased a colour screen independently of a head unit. The screen worked fine but the head unit I got for free was faulty. I then sourced another head unitwith the colour screen from same donor car - but the first colour screen works fully with the second head unit.
Now I have a colour screen that I no longer need. It will only work with a NCDC2013 or NCDC2015 on facelift model. If your car did not have sat nav factory fitted, then this screen will not work without other modifications. However, if you have sat nav with mono (half screen) and 2013 or 2015, then this screen easily fits into place in your dash giving you the full enhanced colour screen with maps, full trip display, etc.
Incidentally, the Stealers charge £1050 plus VAT for a new one. I know, because I nearly assaulted the guy who quoted me with a smile on his smug face!!!
Anyway, in part, this is information for anyone wanting to know how easy it is to upgrade. But secondly, how much should I charge when listing it on Ebay? I got mine from Germany so expect market prices there to differ from here.