Actually i heard they set the colour systems on the first pictures taken from mars wrong. As a result the first (sets?) of pictures where far too red.
However Mars still is red just not like the first pictures which showed that te soil and the atmosphere where both bloodred!
Most of the rocky soil is reddish/brown, some is yellow or other color, and the sky looks normal (whitish).
You can see the differences for yourselves if you compare pics.
http://mars-news.de/color/blue.html
 Pic. A, Viking 1, Nr. 12b069, 29. August 1976, 12.65 locale Mars time This picture was created with color-correction derived from the filter response data. (click on picture to view it in original size) All Viking and Pathfinder images courtesy of JPL/NASA/Caltech. |
 original data without correction |