Seems to me Graeme that you have paid the correct AP of £645 (£495 + £150) for an ST Line and that is what you have received. Red paint is £250 extra on the Puma options list and the dealer would have been rather stingy looking for extra payment for that. I got my paint colour for the Focus ST Line X at no extra charge, the RRP was £550.
Happy motoring…beep beep.