This 3D perspective view is a composite of both HiRISE and data from CRISM, another instrument onboard MRO. This view covers a small patch of ancient Martian real estate in Terra Sirenum.
CRISM collects spectral data that can be used as a chemical fingerprint for the upper most surface. This information suggests that this small patch of surface is covered with salts (chlorides) represented in green and water-rich clays that appear in blue.
CRISM colors can be added to high-resolution images to enhance our knowledge of these materials. They also match nicely with the surface features in our HiRISE image. For example, a fissure near the center of the image may be a a clue to the origin of the salts… [More at link]