I give credance to this color image of White Rock because it corresponds roughly to the color image produced using the wide-angle imager on MGS:

"White Rock" of Pollack Crater
MGS MOC Release No. MOC2-264, 4 December 2000
http://www.msss.com/mars_images/moc/dec00_seds/pollack/

See the color image on this page. This is an approximate color image since MGS does not have a green channel, but estimates it from the red and blue channels.
Note that in this color image the dark areas also have a dark bluish cast.
My expectation is that when the THEMIS visual imaging team produces a color image of this area the dark areas will also have a bluish cast.
I don't think the whole story has been written yet about the composition of White Rock since the TES instrument used by Ruff et.al. only had a 3 km resolution. They describe their work here:

MARS' "WHITE ROCK" FEATURE LACKS EVIDENCE OF AN AQUEOUS ORIGIN.
Lunar and Planetary Science XXXI 1945.pdf
http://www.lpi.usra.edu/meetings/lpsc2000/pdf/1945.pdf

As they state in this abstract the pixels that covered White Rock contained both light and dark colored material. They assert they remove the spectral contribution of the dark material but there is uncertainty in how much is composed of the dark material and how much of the light material. As you can see in the high resolution images on the "White Rock" of Pollack Crater" page, quite a bit of the light colored areas are still interspersed with dark material, perhaps dust. And as we discussed before a quite thin dust covering, perhaps on the scale of only microns, can remove the spectral signature of carbonates.
The assertion that White Rock is compositionally no different than surrounding light colored areas is also made dubious from this released THEMIS IR image:

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

White Rock appears anomalously dark in this IR image either because it is anomalously bright or because it is anomalously cool compositionally. And it is clear it is more so than the surrounding terrain outside the crater.

The full THEMIS IR data on White Rock has been released:

http://themis-data.asu.edu/img/I01061001.html

THEMIS has a 100 m resolution in the IR. I would be more confident of the IR results if they were taken from this THEMIS data where the pixels covered individual light-colored ridges of White Rock without including the intervening dark lanes.

Bob Clark