title_body: Did Kindle contrast get better or is my old Kindle growing old?
upvoted_answer: Apparently E-ink does age due to various physical processes. There is
  lost of contrast (greying), but also freezing of some microcapsules to
  the black state where they are kept too consistently in that state (typical
  for some parts of device state display which stays on-screen).
  
  I am not a specialist, but you can get more (layman level) details
  on the web, such as the article Aging of e-ink screens, which come
  with other articles on display technology.