Why did they discontinue the darker color of the iPhone 5 in favor of the Space Gray?
I am not 100% sure, but I believe I read somewhere that the Silver model is raw aluminum while the Slate model was sprayed black/slate, so it scuff easier.
With the space gray model I believe they are now adding color dye to the aluminum, instead of spray, but with this process you can't add too much dye to the aluminum otherwise it will not come out right, same goes for the Gold model.