Try using this site, it correctly tells me mine is a Four: http://www.vindecoder.net/ Edit: FWIW, it has my rear brakes wrong.
IIRC the Toyota Owner's website should also identify the model... at least, I'm pretty certain it labeled mine as a "Prius Two" and even showed the correct color.
Now that makes sense, as I thought the "one" could only be purchased as a fleet veh? Is that still true? Is it even made anymore?