Color themes for different colored iphone ? Oh please no.
Thats just not the way apple works I think.
Maybe you know this, but in iOS 7 the whole look will change based on the wallpaper because the transparent gaussian blur effect that overlays the phone UI, and that is a very elegant way imo.
And this is as good as it gets in terms of customisation on stock iOS.
Seriously, it's probably like that for design reasons. As others have said, you can alter the look with your wallpaper.