An article to be published in Science also gives a color image of White Rock:

Morphology and Composition of the Surface of Mars: Mars Odyssey THEMIS Results.
Published online June 5, 2003
http://www.sciencemag.org/cgi/conte...tract/1080885v1

in which it is asserted that White Rock is actually red.

The image from this Science paper is copied below. You'll notice it has a decidedly unnatural appearance. I wonder if the method the THEMIS visual imaging team used in the prior THEMIS color images of calibrating using Hubble color images was not used on this image.
Note also that there is little contrast in color with the immediately surrounding area. This is in conflict with prior MGS and Viking images that show the immediately surrounding area with a dark bluish cast:

Martian crater lake may have harboured life
http://www.gla.ac.uk/press/releases/originoflife.html

"White Rock" of Pollack Crater
MGS MOC Release No. MOC2-264, 4 December 20
http://www.msss.com/mars_images/moc/dec00_seds/pollack/

And this page has a thermal infrared image of White Rock that shows it to be much cooler than the terrain even outside the crater:

Pollack Crater, 'White Rock'
http://themis-data.asu.edu/img/I01061001.html

This page in the caption ascribes this to its being brighter than the terrain outside the crater:

Odyssey/White Rock
http://mpfwww.jpl.nasa.gov/odyssey/gallery/martianterrain/PIA03862.html

However, the page on the visible light release suggests that White Rock actually is not white but only looks bright in comparison to the dark material in the crater, which would imply it is not actually brighter than the terrain outside the crater:

White Rock (Released 19 April 2002)
http://themis.la.asu.edu/zoom-20020419a.html

Either it is anomalously bright in visible light which would once more raise the possibility that it is an evaporite deposit, sulfate or carbonate, or it is not and its anomalous darkness in infrared is not due to its brightness but its internal composition, which would once again raise the possibility it consists of an evaporite deposit.

Bob Clark