There's way to much misinformation going on here. So I will tell it the way it is.
All the current eink devices that use a 6" screen use the EXACT SAME Vizplex screen. These devices include the 505, 700, K1, K2, Gen3, V3 (and derivatives such as BeBook and EZ Reader) and others. Now that we have that important fact out of the way, what can be different is the controller use to drive the screen and the software to drive the screen controller.
As for the K1 & K2, the K1 & K2 have different screen controllers and software to drive these controllers on the VERY SAME SCREEN. There is nothing new about the K2's screen. As for the contrast issue, that's most likely a software issue. But I am not 100% sure.
So before you go off and say the screen on the K2 is not the same as the K1, remember, it is the same. The screen controller and software are what is different. Think of it like having a Wii and an Xbox 360. If you use them with the same TV, then you have the same screen but different electronics/software behind the TV driving what you see.
And for those that do not still understand, go stand in the corner till you get it.