The problem here is well-documented in the literature.

The first Viking images were colour-balanced so that the American flag, and other targets on the Viking spacecraft, came out the exact colour they would be on Earth.

Later, it was realised that the colour of then targets depends on the colour of the lighting, so the images were reset to their "raw" data values, giving the "orange" sky.

With time, the callibration was tied down to give the dull tans we live with today.

No conspiracy, no coverup, just a mistake...

This stuff is well-discussed in the literature and on the internet. Don't try and puff it up!

See Don Davis' website for some info on colour