I bought two iPhone 5 last year, one for AT&T and the other for Verizon. The AT&T version screen would look a deep tinted purple when viewing in portrait, but normal if turned to landscape. My Verizon version, the one I'm using now, looks normal in portrait mode, but purple tinted in landscape. Needless to say, I ended up selling the AT&T version.
I would assume the screen is mostly identical for the 5s, but I could be wrong. Are you seeing a purple tint on yours? Does it change when you view the phone in landscape? Sent from my iPhone 5.