(See my new, improved site on the K2 and these issues)
DecalGirl.com has a variety of Kindle skins. While most have purchased these for general aesthetic reasons, I decided to purchase a couple of dark skins to see if my theory about darkening the bezel area would trick the brain into seeing the Kindle screen as lighter. I purchased the Kindle9000 and the Dark Burlwood skins. So far, I've only tried the Kindle9000 skin and it definitely accomplished my goal. It makes the screen look almost like it's glowing. The transformation is quite impressive. Others have tried different skins and most have had good success.
For the purpose of aiding readability, I suggest a uniform or subtly designed, very dark skin - something that won't distract the eye when reading.
For those looking for more information on this optical effect, see:
(thanks to "Art&HistoryFan" on the Kindle discussion boards for this post:
And for those who want to follow this thread on the Amazon discussion boards