  The search for extrasolar planets has already detected rocky planets and
several planetary candidates with minimum masses that are consistent with rocky
planets in the habitable zone of their host stars. A low-resolution spectrum in
the form of a color-color diagram of an exoplanet is likely to be one of the
first post-detection quantities to be measured for the case of direct
detection. In this paper, we explore potentially detectable surface features on
rocky exoplanets and their connection to, and importance as, a habitat for
extremophiles, as known on Earth. Extremophiles provide us with the minimum
known envelope of environmental limits for life on our planet. The color of a
planet reveals information on its properties, especially for surface features
of rocky planets with clear atmospheres. We use filter photometry in the
visible waveband as a first step in the characterization of rocky exoplanets to
prioritize targets for follow-up spectroscopy. Many surface environments on
Earth have characteristic albedos and occupy a different color space in the
visible waveband (0.4-0.9 microns) that can be distinguished remotely. These
detectable surface features can be linked to the extreme niches that support
extremophiles on Earth and provide a link between geomicrobiology and
observational astronomy. This paper explores how filter photometry can serve as
a first step in characterizing Earth-like exoplanets for an aerobic as well as
an anaerobic atmosphere, thereby prioritizing targets to search for atmospheric
biosignatures.
  Key Words: Color-color, Habitability, Extrasolar terrestrial planet, Extreme
environments, Extremophiles, Reflectivity.
