Nick has placed a segment of "brightlands" right next to White Rock in Pollack Crater for comparison purposes. The White Rock formation looks dull gray compared to the bright tan color of the comparison region.
Closer images are (or were) available from the same Viking image global views. A comparison from those images showed that White Rock was at least as bright as nearby light-toned areas under approximately the same illumination. The problem with the comparison Nick used was that the "brightlands" were illuminated more than the Pollack Crater area.
But in fairness, I did another comparison today, using Malin's global mosaic (assembled from red images only). In that context, it appears that White Rock is about the same brightness as the general floor of Shiaparelli Basin.
See it here
Space/Science » in reply to Which part in your image is White Rock?
You got it~!