I've just measured my Kindle Touch, the result is identical to 2 other K4 I've tested(~dE0.5 with CIE2000 standard, about 1% difference for both bright/dark states), all 3 are slightly better in the dark state than the K3(slightly darker). So either I just get lucky every time I buy a K4 or most of the reports of the "worse" screen is caused by some other factors.
For those who have not check out my previous mockup images, take a look at my last 2 posts on
page 5, and make sure that it's not the bazel that is affecting your judgement on the contrast of the screen.
Visual perceptions are very easily fooled!
If you're 100% convinced that it's the screen and not any of the other factors, most likely you won't be getting a better screen by exchanging it, because apparently all the K4s I have test(three of them so far) all have very good unit to unit consistency(1% brightness difference), and I bought them about half a month apart from each other. I would suggest those who have "screen issues" try out one of those dark kindle skins or a dark case that wraps around the kindle to see if that fixes it.
It's also worth pointing out that few who have the instruments to objectively measure their(as far as i know, Blog Kindle & me) K3 & K4 screens share the same conclusion - K4 screens are not inferior to the K3s, they have the same screens. Either that or we're just consistently getting "lucky".
p.s. if the screen bothers you alot and you happen to be in NYC area, I'll be happy to meet up with you at a coffee shop and give you a quick readout from my spectro to get to the bottom of your issue