I have never seen anything like this. What we are seeing are many different kinds of materials in two image frames (mosaic by Emily Lakdawalla). The shiniest textures seen here are more than likely water ice, the darker material may be tholins (a theoretical substance predicted by Carl Sagan himself) and frozen carbon monoxide — but we don’t know for sure.
Thus far, Pluto is so unexpected and so many times more exotic than I would have ever guessed.