I'd say theese are both due to shading.

The second one, E15-01720 is given away from the crater that looks like an event horizon in the upper left corner of the strip.

The first image, E14-00339 gives no such obvious clues but from the looks of the central of the 3 big gullies in this complex, it's also shading. You can see the walls of the gully between shaded areas and the 'color' has very little contrast with the surrounding slope face. The sun is almost directly up slope (within 15 degrees) of these relatively rough and deep gullies (neither good for illumination).

As Nick has explained before, MOC normalizes it's images where the brightest pixel is registered as white and the darkest as black. This is why things that aren't necessarily black as seen by the eye look VERY dark in MOC images.