Yes, thank you both. It looks like again (T68) I'm the lucky "winner" of a defective unit
My T68 is perfect from this point of view, the backlight is even, no issues whatsoever (except for the lack of lower brightness levels of course).
I would be fine too with the shadows at the bottom, but colors showing make my eyes thing they're super tired and they're trying to compensate them, making it worse.
Oh well, I'm not sure when I'm going to find a reader that I can like ...