Don't do gunmetal mate it's the worst colour Nissan had for the zed your zed is looking good so far, give it a unique colour to set it off
If you want to play it safe go for a darker grey. There was a post on quartz grey, the 370z colour that could work
Or a dark blue, not quite as dark as midnight blue. Something like the blue on the new 6 series. Imperial blue I think.
Or metallic red. The Mazda metallic red could work well on a zed
Or if you want to stand out then go for something like bmw San Marino blue on the m5/m6 individual or m4 sakhir orange. A guy in my area had his r33 sprayed in San Marino blue..... Wow..... Looked the part