Deimos (Natural Colors; credits: NASA/JPL)

Caption NASA originale:"Color pictures of the two Martian moons have confirmed Earth-based spectra by also showing both satellites to be gray. The Viking imaging data showed the surfaces to be uniformly gray over the complete surface to a resolution of a few hundred meters. No significant color differences were seen on either surface, including areas around craters and those within the bright albedo features on Deimos.
The color indicates composition is of a carbonaceous chondritic material. Deimos, here, is at a range of 2100 km from the Viking 1 Orbiter. In these pictures, color differences have be en exaggerated; most of the color differences are due to noise or are artifacts of the processing, especially around craters and the limb".