According to Macrumors, some iPhone 4 users are reporting display discoloration issues with their devices. The Retina Displays on their iPhones show brown or yellow discoloration which isn’t a good sign since iPhone 4 is already running short on shipments so replacements wont be available right now. This is what a user found out when visiting a Genius Bar.
A ‘significant’ number of users are facing this issue as per Macrumors. If this becomes a widespread problem, it will be a significant blow to Apple’s claims about how awesome the Retina Display is.