One of MRO’s ongoing campaigns is a search for new impact craters. At high latitudes, such craters often expose ice, which appears bright in HiRISE enhanced-color images. This image was targeted to look at a candidate new crater on a lobate apron. Such aprons are often ice-rich, but the crater shows no bright material that would indicate ice.
Why not? The most likely reason is that the crater simply didn’t dig deeply enough. [More at link]