There is an issue about reading pdfs on my kobo glo, which should be almost the same as the aura. When I slide to read a pdf file when it's zoomed in (a book with two columns) the small rectangular Window who show you how to navigate on the page, it leave a shadowed rectangular when the zoom options fadeout, it's like the whole page has less contrast (faded text), and only the area which contained the Window keep using a good contrast! I have tried turning the reader into sleep mode, when i turn it back on, it refresh the entire screen and it looks much better!
I think there is a problem with the screen refresh when reading pdf files, the developers should really focus on this part of the reader, it's really frustrating reading pdfs on the kobo glo. I hate lcd, it hurts my eyes and most tablets are cumbersome and heavy for reading outside, add to that, you won't be able to see anything under a bright sunlight.