Meandering through the center of the paonrama is a rill, or gutter, if you will, creating a depression. The color differences in both color panos is most likely due to the different angles to the sun which show up as sugary goodness (high albedo)on the right side (maybe). The hirise images i have been studying do show some color differences in the direct vicinity of the lander. Not sure if they are related but it's something to think about.