From the "Viking Archive" - Viking 1: late afternoon

This is a Viking One late afternoon view on a fairly clear day. The bright sky near the Sun is apparently a lighter bluish color due to 'forward scattering'. The blue seen here is probably more camera induced than real. On Mars the 'Raleigh Scattering' which colors our sky blue is greatly diminished by the low atmospheric pressure. Although no obvious clouds were reported, The horizontal texture in the sky to the left of the overexposed region might just be some weak cloud detail.