One advantage of THEMIS over TES is its higher resolution.
The argument that White Rock does not consist of evaporites based on TES measurements is summarized here:

MARS' "WHITE ROCK" FEATURE LACKS EVIDENCE OF AN AQUEOUS ORIGIN.
Lunar and Planetary Science XXXI 1945.pdf
S. W. Ruff, P. R. Christensen, R. N. Clark, H. H. Kieffer, M. C. Malin, J. L. Bandfield, B. M. Jakosky, M. D. Lane, M. T. Mellon, and M. A. Presley.
http://www.lpi.usra.edu/meetings/lpsc2000/pdf/1945.pdf

Note that the Ruff et.al. report states that only 8 of the pixels in the TES image actually covered White Rock and the light colored regions were interspersed with the dark colored material.

The THEMIS IR image data on White Rock is available here:

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

Note that White Rock is anomalously dark in this THEMIS IR image, which means that it's cool. Note as well that it is darker in IR, i.e., it's cooler, even than the terrain outside the crater.
THEMIS has a 100 meter resolution and since White Rock is fully covered by the THEMIS image, it's 12km by 15km size would result in 120 x 150 pixels or 18,000 pixels, a more than 3 orders of magnitude improvement in the amount of data that could be analyzed to determine White Rocks composition.
I'd like to see the THEMIS analysis on those pixels covering White Rock that had the least amount of covering of the interspersed dark material.
My contention is that those would be brighter than the usual bright areas on Mars.

Bob Clark