This needed a little repetition because it was looked over in William's thread. These links are courtesy TheRealDeal News, inc.
"If you ask a Meteorologist about the reason for blue sky on Earth, he will name the Rayleigh scattering.
If you ask a NASA Scientist about the reason for red sky on Mars, he will name the fine dust in the Atmosphere which scatters light like during sunset
But there are not always dust-storms on Mars which pollutes the Atmosphere.
So there have to be also days which show blue sky!
Even NASA / JPL writes in this article about the possibility of blue sky and 3 days before Pathfinder landed, this note appeared in a press release by
"If dust diffuses to the landing site, the sky could turn out to be pink like that seen by Viking," says Philip James of the University of Toledo.
"Otherwise, Pathfinder will likely show blue sky with bright clouds."
And the pictures of this clear blue sky do exist! Especially from the Viking Mission, as you can see on the next page"
About the sun dail business, it's been done before:
"This is the color calibration table on Pathfinder.
It's a simple sun-dial with some color spots on it.
click on the images to enlarge NASA said, that they will sent the first sundial to Mars with the Mars 2001 Mission. This is wrong, as you can easily
see that there is already a sundial fixed to Pathfinder!"
And.. last but not least, they changed the pics on the Viking as well: