From what I could tell living under the approach to LGA rwy 4 in Brooklyn, it did seem to be a 321 -- definitely a Spirit paintjob as opposed to US -- and that old, familiar A320 family howl...
I saw it at FLL last Saturday. That silver/gray 321 was surrounded by the older fleet in white and blue. I prefer the white and blue, but the wife liked the silver and black. No matter what color, it sure stood out!