Thanks woodlock.
Looks like greenish tinged dust accumulating in areas of high aerodynamic trapping potential.
Or, why would lichens or whatever prefer potentially shaded areas?
And who's to say a putative Martian fauna would be green? On earth, photosynthesis uses(absorbs) blue and red wavelengths and rejects(reflects) green, a color close to the peak spectral intensity from the sun.
On earth the sky is blue due to scattering, on Mars this is NOT the case and if you're capable of accepting this fact, you might have to re-think green exposed flora on Mars as being plausable.