I read that it was the new Pearl screen;
http://www.youtube.com/watch?v=jxtEdyjda6s
I think on the KDX Graphite page it stated 10:1 contrast.... and in this video the guy said that the new screen could reach 10:1 contrast.
And here:
E Ink details new display tech behind Kindle DX
E Ink has revealed the technical details behind its new e-paper display, which is used in the next-generation, just-announced Kindle DX. Dubbed Pearl, the new display tech increases the contrast ratio by 50 percent compared to the outgoing technology. The new e-paper uses an electrophoretic display and is based on current Vizplex designs.
The text is said to be crisper, like the difference between newspapers and paperback novels. This makes the screen and text much more visible in the outdoors as well, E Ink said. Images can be more clearly reproduced thanks to 16 gray levels.
E Ink Pearl also has improved energy efficiency, though exactly how much more efficient it is hasn't been divulged.
http://www.electronista.com/articles...new.kindle.dx/