The Nili Fossae region, located on the northwest rim of Isidis impact basin, is one of the most colorful regions of Mars.
The colors over many regions of Mars are homogenized by the dust and regolith, but here the bedrock is very well exposed, except where there are sand dunes. The rocks also have diverse compositions, which produce different colors in HiRISE infrared-red-blue color images. [More at link]