2002-03 are the best years for the 9-5 generally. Got all of the improvements of the mid-cycle enhancement, before they started deleting stuff to cut costs.
The '02+ Aero's have better seats -- the '00 and '01 Aero's have the same seats as the other 9-5s.
But, as you're looking at a five-speed Aero, the main advantages of the '02+ models are not particularly relevant: (1) a much improved five-speed automatic, and (2) suspension and handling improvements which brought the base models up to '00-01 Aero levels.
Colors I'm not so sure about. I know that Imola Red was available for the Aero's in '00-'01. I don't know if I've ever seen a 9-5 Aero in either Cayenne Red, Chili Red, or Merlot. Of the three, I would bet on Merlot, though.
You can get an Aero in the best 9-5 color of all, though - Cosmic Blue.
Why all the sudden interest? Not happy with the ng900?