Original factory magazines were all blue, regardless of the finish. I passed up a nickeled 39 once before I knew that. The +P question is still open: S&W says no, but perhaps a lot of that is CYA. I wouldn't shoot much +P in my 39s, but I'd sure carry it.

Edited to add: Factory Model 39 magazines are stamped S&W or 9mm S&W on the bottom of the floorplate. All except one: I have a 39 magazine whose floorplate apparently went throught the stamping machine upside down: it's stamped S&W on the inside.