Color snap-shots from Viking 1 (7)

"...In the course of the Martian Year an important surface change was observed at the Viking 1 site. During the Winter months a thin layer of frost formed. This is documented by comparing two black and white pictures, the first taken early in the mission in late Martian Summer and the second taken months later in late Martian Winter.
Patches of receding frost were visible in the 2nd picture. During the height of Winter, frost probably covered the entire surface.
This picture is a color image of the frost, looking across the spacecraft. The colors purposely have been distorted slightly to enhance color contrast.

The frost persists at temperatures higher than those required for frozen Carbon Dioxide (dry ice).
It may be Water Ice or a Carbon Dioxide clathrate, a crystalline mixture of H2O and CO2".