That's a pretty poor picture in terms of photo quality.
It's one of a couple things:
- Reproduction label and board was transplanted which I would say is most likely
- Something was wrong with the cartridge and someone sent it in the Nintendo and received that as a replacement (kind of like the Rage Wars carts being Black at retail and Gray received when sent in for repair)
- (and I'm not sure of this even ever happening) A very early run of the game and they used a grey shell instead of a gold shell
- (and again, not sure if this has ever happened) A NFR Majora's Mask that was one of the first one's made and before they added the "Not For Resale!"
Thee only gray Majora's Mask, like Cristian said, is the Not for Resale, and it will say "Not For Resale!" on it, like in my avatar.
The PAL version is also Gold, so I know that's not it.
Unless actually seeing a high quality picture of that cart, or you seeing it in person and comparing the gloss of the label against another cartridge, it's kind of hard to tell what's going on with it.
If it does turn out to be an actual Majora's Mask that was made in a grey shell, and not a transplanted board with a repro label, it could be worth quite a bit, but it might be hard to tell if that is the case with this or not.
Edited: 01/18/2013
at 07:35 PM
by Vaosu