On a related side-note here, I recently started a thread asking about color and texture variances in the bolt carriers on the Sport II's. Mine has a rougher surface texture, and a greenish hue to it (especially visible under extra light), than any of the others I've compared it to. One or two other guys here said theirs looked the same way, but most said theirs had the smooth, satin black finish that seems to be most typical.
So it would appear that it the receiver halves aren't the only parts S&W is puitting out with odd color variations.