It seems the black iPhone 5 is prone to ugly scratches.
Pocket-lint notes:
Ditching the glass back and reducing the thickness of the glass panel on the front has affected the design of the metal band around the edge of the iPhone.
It is now chamfered and while that looks pretty, we’ve already noticed that on the black model the edge has started to wear, revealing the shiny silver aluminium metal underneath the “slate” coloured coating and, indeed, we’ve witnessed it on two separate models, ruling out a fluke manufacturing error.
iFixit’s scratch test on the black iPhone 5, meanwhile, can be viewed below.