The blue areas here seen here might be related to the blue tints seen on some rocks at the Pathfinder site:

Photographs show red, white and blue rocks on Mars
http://www.floridatoday.com/space/explore/stories/1997b/072997c.htm
"In panorama photos taken by Pathfinder of its landing site, there
is a striking two-color appearance on dozens of rocks, Smith
said.
"You divide the scene into two parts - the red part and the blue
part,' he said. 'There is a very clear difference between the red
side and the blue side.'
"Smith said that the blue side is on the east side of the rocks,
suggesting that the sometime-ferocious wind storms on Mars
may have scoured off a layer, uncovering the color. The west
side of the rocks, protected from the wind, are red, probably from
layers of Martian soil, he said.
"The strong wind comes through and it could have sandblasted the one side of these rocks," he said. "

This is discussed further in a report given at the 31st LPSC:

Blue Mars
http://www.lpi.usra.edu/meetings/lpsc2000/pdf/1938.pdf

Bob Clark