I just traded my iPhone 6 for a 6+ last week and I noticed a spot under the screen. It's definitely not on top or anything I can wipe off. It's like it's behind the screen and causes a small round shadow visible behind any solid colour. It's not visible in photos etc because it blends into the shading etc. But any white or light background I can see it very well. It's not large though, only about 1mm x 1mm. I can see it as a grey shadow that doesn't move when I scroll what's on the screen... and somehow now that I see it, I can't seem to UNSEE it! Should I take it back and have them exchange the phone? I am worried if there is a screen issue maybe it will get worse over time. I do have apple care on this but it's virtually brand new I only got it last week.