Last year, many early iPhone 4 buyers had issues with yellow patches on the display, which Apple explained was because they had been put together very recently and the glue needed time to finish drying.
The problem this time around appears to be different, as it affects the entire screen, not just small areas.
While some people are suggesting this is an intentional calibration change on Apple's part, that wouldn't explain why some iPhones don't seem to have the problem at all and others appear to have either a blue or green tint, rather than yellow.
Others have speculated it's a result of Apple getting displays from multiple manufacturers. It may be that the screens are the component which was causing the rumored production shortages last month.