3GS: Black
4: White (yeah, I waited for it)
5: White
6S: Space grey (because the white bands look ugly on the other colors. Would've gotten gold)
I really wish for a nano chromatic iPhone. The color combinations on iProducts are kinda boring nowadays, especially since every Android OEMs now copied the same color scheme. Metallic green, or blue would be sweet, but I can see Tim Cook as a boring man that prefer streamlined and simplified supply chain.