Re: It's been repainted
It depends whether it is original Alfa paintwork or not. The fact that only 1 panel is changing colour would suggest that it may have been resprayed at some stage and is not original but without seeing it is hard to tell.
If you take it to your Alfa dealer I guess he will just claim it has been repainted. You could take it to a non-Alfa paintshop first and play dumb, ask them about the slightly different colour, and they should tell you whether or not its original or repaired. Then go to the Alfa dealer.
If it has been painted then you need to find out where (previous owner) ... it may even be that it was repainted new pre-delivery!