Problem: opaque iPhone back plate. Solution: replace with transparent back plate from iFixIt.
Removal of the old back plate was easy enough -- just two pentalobe screws to remove. I did run into problems during installation of the new back plate: unlike what's been said in the installation video, the lens protective film was on the *inside* of the back plate, not on the outside. I had initially installed the backplate without removing the protective film, which caused washed out photos and and ill fit of the back plate. After removing the plate and taking a second look, I found the protective film, removed it and reinstalled the plate. Works like a charm now!
Be sure to check both the inside and the outside of the camera lens for protective films. In the instructions video, the film was on the outside, but in my case the film was on the inside.