First, you cannot back light an opaque eInk screen. Not going to happen.

Second, whenever a top layer of plastic is put above the screen for lighting purposes, you can expect inconsistencies like splotches and discoloration. Light is tricky to get right with a reflective layer of plastic on top. So expect that as long as Amazon continues to insist on using such a lighting layer there will be a degradation in readability of the eInk screen. Even without the splotchiness and/or discoloration, an extra layer of plastic will blur the eInk screen a bit. No plastic is perfectly transparent or invisible.

Yes I agree that the light layer is poorly designed and implemented in all the PWs, Voyage, and I assume the Oasis as well. I wish they would offer the Voyage without the light layer, though I know they never will. I would rather Amazon improve the physical quality of their basic Kindle with higher resolution screen and better ergonomics instead of focusing on a bunch of firmware features that I could care less about. Most of those firmware features are there because it helps Amazon to sell you more books.