The following applies to IJA gray in many ways, and check the j-aircraft sights research section and scores of photos to pick your gray.
As I said in an early (and too-long post), I just discovered, after reading a lot of research on the site j-aircraft.com, Poly Scale Concrete, and just used it on a A6M3 Type 32 (clipped wing), the old Tamiya kit. It was beautiful, and matched as well I could be done, by comparing the contast of white against the gray, using black and white photos. As I said, we have been led to believe that these planes were painted an almost white gray, and that is not the case. They came from the factory, depending on which of the two factories -- Mitsubishi or Nakajima -- with different shades of gray. The concrete, which is recommended by a number of modelers who specialize in IJN aircraft, should be lightened with a few drops of white, and it gives a slightly, what? Yellowish gray? Or maybe the tiniest hint of green. But I'm told this color ranged to a clearly green-gray, which can be made by lightening British Sky Type S, or if you want to proper cockpit color, darken Sky Type S (Tamiya's) with a little sea gray.
I'm doing a second Zero now, a Hasegawa Type 22, and for the lower color (the top is green) I'm going to use a little different gray, and see what's best. It'll take a little more research, but if you are going to paint a gray Zero, or do any Zero at all, go to the web site I mentioned. It's the best you could ask for.
Tom