Deimos (Natural - but enhanced - Colors; credits: NASA/JPL/Univ. of Arizona)

HiRISE captured this enhanced-color image of Deimos, the smaller of the two moons of Mars, on 21 February 2009.
Deimos has a smooth surface due to a blanket of fragmental rock or regolith, except for the most recent impact craters. It is a dark, reddish object, very similar to Phobos.
There are subtle color variations — redder in the smoothest areas and less red near fresh impact craters and over ridges or topographic highs (relative to its center of gravity).

These color variations are probably caused by the exposure of surface materials to the space environment, which leads to darkening and reddening. Brighter and less-red surface materials have seen less exposure to space due to recent impacts or downslope movement of regolith.
With an image scale of about 20 mt/pixel, features 60 mt or larger can be discerned.