This weird shot from Opportunity, referenced by recent traffic casualty Sandy Moondust, looks more like a Woodstock-era concert poster than a bit of scientific data.

The photo is a composite image of hematite concentration (via Mini-TES) overlaid onto a visible-light image of the surface. High concentrations of hematite are indicated in red, shading through green to lower concentrations indicated by blue. The bedrock outrcropping appears visibly lower in hematite than the soil. Some of the blue blobs closest to Opportunity look to me like beach-ball prints, where the soil was disturbed by airbags during the rover's landing...which if true is a curious bit of data, since it implies the soil itself is low in hematite but for a very thin layer at the surface.