Out of the blue I just noticed when I rebooted my iphone last night that while in the black apple logo screen the top left corner looks lighter and slightly yellowish and I can find no explanation since in my hands it has never gotten more than a couple short-height falls and on carpeted floor on top of it. And it has always been in a case. Can there be any reason other than a fall for this? (I've started suspecting that someone else might have let it fall maybe?) And more importantly, is this serious and something I'd want to get it checked for? I'm under Apple Care+ until next year, so will this cover it? Help?