I think what you are seeing is refered to as "ghosting". From what I've read on these forums the 505 should have little to no ghosting even though I've encountered little ghosting on both of my 505's. This especially is noticebale when switching from a page that has a lot of deep blacks, like the deep black borders on the menus, to a page that is mostly just text with a grey background.
Since there are reports of people experiencing no ghosting I'm not sure if this is normal but it isn't enough to bother me since after turning just one page, the "ghosting" goes away. Might be a bother if I was reading comics or something with a lot of pictures but I don't. I often do my reading at night and the reader gets kind of cold and I'm not sure if it's a temperature related problem as well.
However, it seems like you didn't have this issue on your first reader? If that's the case, it might be a defect with your screen. The background of the reader to me atleast, looks grey and your first one should've looked just as good as the second one.
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