I'm informed by someone who works with the MODIS system that the passage I cited meant the ice is dark and snow is grey in near-infrared because the ice contains more water than the snow. And bare ground is brighter than snow because it contains less water.

Also, the TES detector in the range from .3 to 2.7 microns on Mars Global Surveyor only collects the *total* irradiance over this wavelength range so it could not distinguish an area brighter at 410 nm as opposed to 550 nm, for example.
However, the Hubble might have sufficient spectral and spatial resolution to make this discrimination. I'll check on that.

It is the case though that the OMEGA spectrometer and the CRISM spectrometer on Mars Express and Mars Reconnaissance Orbiter will have this discrimination capability.

Bob Clark