I believe the display on the 5C and the 5 and 5S are the same. It seems there is a difference in the aspect ratio on the 5C. I don't know if that's the difference. They look the same to me.
If you believe you have a defective display take it in to a Apple store if possible and compare and talk to a genius.
5S display specs
4 in (100 mm) diagonal
(9:16 aspect ratio),
multi-touch display,
LED backlit IPS TFT LCD,
640?1136 pixels at 326 ppi,
800:1 contrast ratio (typical),
500 cd/m2 max. brightness (typical), Fingerprint-resistant oleophobic coating on front
5C spec
4 in (100 mm) diagonal
(9:16 aspect ratio),
multi-touch display,
LED backlit IPS TFT LCD,
640?1136 pixels at 326 ppi,
800:1 contrast ratio (typical),
500 cd/m2 max. brightness (typical), Fingerprint-resistant oleophobic coating on front
5 specs
4 in (100 mm) diagonal
(16:9 aspect ratio),
multi-touch display,
LED backlit IPS TFT LCD,
1,136?640 pixels at 326 ppi,
800:1 contrast ratio (typical),
500 cd/m2 max. brightness (typical), Fingerprint-resistant oleophobic coating on front