After reading Mark Petry's post about the file marks showing on the BB shell, and observing the sloppy red highlights fill in the round openings in the BB shell and elsewhere, I am convinced that this bike has original paint.
Despite the talents of many painters around the world, I have never seen casting marks, or file marks show through the paint on resprayed frames.
Moreover, there isn't a (re)painter on the planet who would do such a nice repaint, but glop the red paint so sloppily in the lug holes.
All the original Cinellis I've seen have sloppy highlight fill, and most have bubbles in areas near the bottom bracket shell.
I agree with Brian that a certain amount of yellowing will occur on original paint from that era. I have seen this particularly where clamps are- on the top tube, and for the shifters on the downtube, but I think that this can be polished away... maybe not, but regardless- I believe that the paint on that silver Cinelli is original.
John Barron Minneapolis MN, USA http://www.velostuf.com
PS- Cinelli Model B's from at least as early as the mid-50's have the typical Cinelli fastback seatstay design.