Incidentally, is it possible that the "greyness" of Sony reader and hanlin is worsen due to the contrast or lack thereof between the white casing and the "white" of the screen itself, while iRex's black case increases the perception of "whiteness" in the "white" of the screen.
I've seen some optical illusions where two blocks of grey appear vastly different but are in fact the same color.
http://en.wikipedia.org/wiki/Optical_illusion
Simultaneous Contrast Illusion. The grey bar is the same shade throughout