The 'brown' in this VIS image is part of the ejecta surrounding Escorial Crater. The material of the ejecta blanket is much more resistant to local winds and remains as a plateau above the lower elevation plains. Sand dunes fields are very common around the north pole. The dunes in this image are part of Hyperboreae Undae.
The THEMIS VIS camera contains 5 filters. The data from different filters can be combined in multiple ways to create a false color image. These false color images may reveal subtle variations of the surface not easily identified in a single band image.
Orbit Number: 60523 Latitude: 77.7042 Longitude: 304.675 Instrument: VIS Captured: 2015-08-06 05:44
https://photojournal.jpl.nasa.gov/catalog/PIA22709