This image is a combination of four taken on July 14 at about 8:07 UTC as New Horizons passed through the Pluto system. The grayscale LORRI image has been enlarged by a factor of three and overlaid with color information from an image taken by Ralph MVIC at about the same time. Nix has an unusual red crater feature on its surface -- and no other obvious craters.
Here are the four component images.
Here are those four component images, stacked, enlarged 300%, and sharpened.