Originally Posted by Magnesus
There was literally none. I had a device with 4 colour Vizplex and now have with 8 colour Vizplex and there isn't any difference between the contrast of those two.
Vizplex = second generation eInk. The number of shades of gray related to the display controller, not the display itself.
Being the owner of a PRS-500, which did have a first generation display, I can say that the Vizplex screens are noticeably brighter. Of course brightness ≠ contrast.