What I and others are doing is refining and testing models of how various surface features form. When the Galileo images first came out we developed models based on warm ice to explain features like we see around Thera and Thrace. The best spectral match is to magnesium sulfate, better known as Epsom salts. When warm convecting ice rises up and hits a salty area it melts at a lower temperature than the surrounding plains. This sort of process might explain regions like Thrace where we see what appears to be melting and liquid-like flows across the surface.
NIMS data indicate a correlation between brown areas and salty spots.
The best candidates for the brown material are iron compounds or some sort of sulfur compound. Both iron and sulfur are relatively abundant in the solar system and have a red appearance visually. Still under development, the Europa Orbiter will use a radar sounder to measure the thickness of Europa's icy crust and possibly determine whether liquid water exists below the ice. An on board altimeter will gather topography data and characterize the tidal response of the surface. Tidal distortions of Europa's crust will be large if there is an underlying layer of liquid water and smaller if the water is in the form of ice.