Ugh, Amazon has some serious quality control issues.
My original Paperwhite had a fairly noticeable blue splotch in the upper right, that gradually fades in a line toward the lower left. Amazon sent me a replacement with an even larger blue/dim spot in the middle of the screen. I finally received a second replacement today, and it seems to have a more even color (although it still has noticeable splotches at high brightness when viewed in a dark room), but the contrast is noticeably worse than either of the other two. Also, on comparing the original with the two replacements, the original seems to have more ghosting, and occasionally under-draws some sections of the screen.
In spite of all that though, it has the best contrast and the most even brightness of the three.
I really don't know which one to keep at this point...