Curiously the screen ghosting has reduced a little more and it's a little brighter. Still the dimmest of the six models I CURRENTLY have. Centre rear row. I might cover the bezel with grey "sticky backed" film as paint wears off. You can see the black plastic that's transparent to the IR used for touch just below bezel.
Rear, L to R: Sony PRS350, Kobo N950C Touch, Kobo Aura HD H2OO original.
Front, L to R: Nook, Kindle Keyboard, Kindle PW3 / Paperwhite 2015 (bought Nov 2018).
Photographed by phone, LED "filament" style room light, not daylight. Front lights are off (H2O) or minimum (PW3). Differences in greyness are larger than the photograph suggests.
The Kobo H2O original is the "brightest". I've compared the PW4 (Paperwhite 2018) and it is nearly as grey as the Kindle Keyboard, greyer than the PW3, I suspect because it's capacitive and not IR touch. Any touch other than IR makes the screen darker, no doubt Amazon think people will compensate with "front light" LEDs.
I guess no-one knows how to make the "home button" be a "next page"?
Reading at night
I find the "filament stick" LED lights less blue than regular LED lamps. They also don't have a SMPSU, which on most LED lamps makes a lot of radio interference on AM. Each stick is about 22 LEDs (mostly blue/violet) covered with yellow phosphor, so two are needed for 115V nominal (North America, Japan) or four sticks for 230V nominal (Mostly everywhere else). Some are dimable. Most are not. Some have a few other colours of LEDs mixed into the sticks to improve colour rendition.
Colour Rendition can be rubbish with cheap CFL and LED even if colour temperature is like "daylight". An LED "filament" lamp in a bedside spot lamp is more like incandescent or halogen light, but 4W rather than 40W so cool. No wakeful blue tinge so nicer than "front lights", CFL or regular LED. The large number of LEDs at lower power means longer life for the phosphor and no SMPSU (which loses 10% of power, can fail and makes Radio Interference).