The pix tend to make the background look whiter than it really is -- it's one of the challenges of e-ink, that it doesn't photograph well.
That being said, it ought to be a fairly light gray in the background, such that if you get it in direct sunlight, it looks nearly white. I do know that the display gets a bit more ... fluid with use, so the contrast is a bit lower when it's been idle for a while, and improves after using it a bit, but that shouldn't take too much use to see, 4~5 page changes in quick succession should do it. Oh, yeah, it does get more sluggish as the temperature drops, so if you're using it in a particularly cold environment, you'll probably see some of that. Hmmm, and a low battery charge can result in the contrast dropping too....