A quote: "The colors in this image are not what a human standing on Mars would see — the presence of dust in the atmosphere would make the scene appear much redder. Instead, the pictures have been white-balanced to show how it would appear under typical Earth lighting conditions. This will help the Earth-centered geologists who are trained to recognize features based on how they look using more familiar light."
An adept user of programs like Photoshop can manipulate the colors of an image to meet any imaginable criterion:
http://www.wired.com/wiredscience/2012/08/curiosity-sharp-ba...
A quote: "The colors in this image are not what a human standing on Mars would see — the presence of dust in the atmosphere would make the scene appear much redder. Instead, the pictures have been white-balanced to show how it would appear under typical Earth lighting conditions. This will help the Earth-centered geologists who are trained to recognize features based on how they look using more familiar light."