I just updated this post with a higher resolution image of this hole in Mars. Click on the image for an even higher resolution version.
The darkness of this hole in Mars is not due to limitations of the cameras. The Mars Reconnaissance Orbiter is usually always able to detect details even in dark shadow. But blowing this image out to reveal details shows nothing. No side walls, no bottom… leading most to consider that this is a sinkhole that fell into a large Martian cavern. Most likely the total lack of detail probably means that the surface around this hole is actually over-hanging a deep pit.
Maybe this is where all the ancient running Martian water drained to. Better watch your step.