I see more misinformed people have shown up in NASA's defense . The color of Mars is only red to the naked eye and through telescopes from Earth . It is a myth that the planet is really red or the sky pink . Here is the article I was looking for that explains how NASA employees were ordered to alter the color photographs of Mars two hours after the images came in . This was not an accident or a mistake on NASA's part . It was deliberate tampering with the photographs to disguise the fact that Mars looks very much like Earth . Below is a few paragraphs from the article and the pictures of the American flag which shows beyond a doubt that the pictures were altered on purpose to make Mars a color it really isn't .
Here's part of the article.
"The "witness" is the son of the scientist in charge of one of Viking’s three historic "biology investigations," the Labeled Release Experiment: Principle Investigator, Dr. Gilbert Levin. His son’s name is Dr. Ron Levin, now also a scientist a physicist -- at MIT.
In the summer of 1976 (when Viking landed), Ron was a newly-graduated high school student, assisting his father at JPL during that incomparable "Viking Summer" (where this writer was also present, covering the extraordinary Viking story for millions of readers of a major magazine, and a couple of broadcast television networks …).
The following is from Levin’s first-hand recollections of the whole affair, recounted in a recent book by science writer Barry DiGregorio -- the remarkable "over reaction" by JPL that occurred in response to Ron Levin’s naive efforts to "correct" what seemed to him that July afternoon to be "a deliberate – if perplexing – methodical distortion of the incoming Viking Lander data" (Mars: The Living Planet, B. DiGregorio, G. Levin and P. Straat, Frog Ltd, Berkeley, CA 1997).
According to DiGregorio’s narrative:
"At about 2:00 P.M. PDT, the first color image from the surface of another planet, Mars, began to emerge on the JPL color video monitors located in many of the surrounding buildings, specifically set up for JPL employees and media personnel to view the Viking images. Gil and Ron Levin sat in the main control room where dozens of video monitors and anxious technicians waited to see this historic first color picture. As the image developed on the monitors, the crowd of scientists, technicians, and media reacted enthusiastically to a scene that would be absolutely unforgettable – Mars in color. The image showed an Arizona-like landscape: blue sky, brownish-red desert soil, and gray rocks with green splotches ...
"Gil Levin commented to Patricia Straat [his co-Investigator] and his son Ron, ‘Look at that image! It looks like Arizona’ [below].

"Two hours after the first color image appeared on the monitors, a technician abruptly changed the image from the light-blue sky and Arizona-like landscape to a uniform orange-red sky and landscape [below]. Ron Levin looked in disbelief as the technician went from monitor to monitor making the change. Minutes later, Ron followed him, resetting the colors to their original appearance. Levin and Straat were interrupted when they heard someone being chastised. It was Ron Levin being chewed out by the Viking Project Director himself, James S. Martin, Jr. Gil Levin went immediately and asked, "What is going on?" Martin had caught Ron changing all the color monitors back to their original settings. He warned Ron that if he tried something like that again, he’d be thrown out of JPL for good. The Director then asked a TRW engineer assisting the Biology team, Ron Gilje, to follow Ron Levin around to every color monitor and change it back to the red landscape.

"What Gil Levin, Ron and Patricia Straat did not know (even to this writing) is that the order to change the colors came directly from the NASA Administrator himself, Dr. James Fletcher. Months later, Gil Levin sought out the JPL Viking Imaging Team technician who actually made the changes and asked why it was done. The technician responded that he had instructions from the Viking Imaging Team that the Mars sky and landscape should be red and went around to all the monitors‘tweaking them to make it so. Gil Levin said, The new settings showed the American flag (painted on the Landers below as having purple stripes. The technician said that the Mars atmosphere made the flag appear that way [emphasis added].’"


As someone who was also at JPL that afternoon, and vividly remembers a similar shock -- when the "Arizona Mars" initially flashed on the JPL monitors was suddenly transformed into a Martian "Red Light District" . I now kick myself for not asking lots more questions.
But, it was 1976 -- and we all trusted our Space Agency back then ….
One of the basic questions that I should have asked involves the physics behind JPL's abrupt color alterations. Or, as Gil Levin put it:
"If atmospheric dust were scattering red light and not blue, the sky would appear red, but since the red would be at least partially removed by the time the light hit the surface, its [the direct sunlight’s] reflection from the surface would make the surface appear more blue than red. There would be less red light [in the direct sunlight illumination] left to reflect. And what about the sharp shadows of the rocks in the black and white images yesterday? If significant scattering of the light on Mars occurred [from lots of red dust in the atmosphere], the sharp shadows in those images would not be present, or at best, would appear fuzzy because of diffusion by the [atmospheric] scattering [emphasis added]!"
Levin was describing the well-known phenomenon of "Raleigh scattering" -- whereby the similar-sized molecules of all planetary atmospheres (be it the primary nitrogen of Earth; the carbon dioxide atmosphere of Mars; or even the predominantly hydrogen atmospheres of Jupiter and Saturn!) all produce blue skies when sunlight passes through them.
If you examine the long Martian photographic record which encompasses hundreds of thousands of images, acquired by dozens of observatories even before the Space age dawned you can see blatant evidence that Levin's right and JPL is wrong regarding the scientifically expected color of the Martian atmosphere."
The rest of the article is here .
http://www.enterprisemission.com/colors.htm