Got the replacement Kindle today (batch 503) and, its pretty poor. The screen is very yellow, alot different to the 'white' screen of my other shadows at bottom Kindle or the one with the grey line at the top (both of which were 'white' on max brightness). Also, the 503 replacement has clear marks of cleaning product run across the screen and on the black bezel. So, I'm 100% certain it was a refurb. It also had the shadows between LEDs like my original PPW had. I think like others said, I'm going to return completely and order a new one - hopefully they've fixed the grey line screen alignment prob.
See pics here - replacement on left and misaligned screen it replaced on right: