No difference except the color. There is only one (functional) version of the Polar Pacer Pro (not to compare with the simpler version "Polar Pacer").

Also as described, there is also no different "size" of it, like we can have for other models (Vantage, ...), it is "one size".
In the package though, there are two arm band (for the second part with the holes) of different size.

Usually the lowest price you can get (these current days) is with the White/red version, probably because there is less demand.