This enhanced-color view shows gullies in an unnamed crater in the Terra Sirenum region of Mars. The image was taken by the Mars Reconnaissance Orbiter on Oct. 3, 2006. This scene is about 830 feet (254 meters) wide. The upper and left regions of this scene are in shadow, yet color variations are still apparent. The high signal to noise ratio of the orbiter's high resolution camera allows for colors to be distinguished in shadows. This allows dark features to be identified as true albedo features versus topographical features. An albedo is the ratio of the light reflected by a planet or satellite to that received by it.
Image Source: www.nasa.gov/multimedia/imagegallery/image_feature_692.html