This report presented to the 7th International Conference on Mars suggests they *might* have seen one of the more common south polar geysers actively venting:

HiRISE Views of the Sublimation of Mars’ Southern Seasonal CO2 Cap.
C. J. Hansen1 , C. Okubo2, A. McEwen 2, Shane Byrne3, E. DeJong1, K. Herkenhoff3, M. Mellon4, P. Russell5, and N. Thomas5, 1Jet Propulsion Lab, Pasadena, CA 91101, 2University of Arizona, Department of Planetary Sciences, Tucson, AZ 85721, 3USGS, 2255
N. Gemini Dr., Flagstaff, AZ 86001, 4University of Colorado, Boulder, CO, 5Physikalisches Institut, Universitaet Bern, Schweiz.
Seventh International Conference on Mars 3364.pdf
http://www.lpi.usra.edu/meetings/7thmars2007/pdf/3364.pdf

From the report:

"Our approach was to attempt to detect dust
plumes by acquiring stereo images separated by a very
short time interval. Near the pole the orbit groundtracks
are closely spaced allowing us to image a given
location with just one orbit (~2 hour) separation. Any
geyser-like activity should be detectable in stereo images
as a plume rising above the surface. The hypothesis
that every spot is a site of gas jets [3,4] implies
that the probability of catching a geyser in action
is very high."
HiRISE Views of the Sublimation of Mars’ Southern Seasonal CO2 Cap, p. 1.

"At one location in the Manhattan Island region, using
our stereo imaging technique, we may have captured
a geyser in the process of eruption. It is a tenuous
detection at best, very near the limits of the camera
capability. The putative plume is not high above the
surface (< 10m high) and is optically very thin. In
stereo small bumps on the surface can be observed that
may be the site of other gas jets. Figure 5 shows the
bumps and small fans that may be the initiation of the
gas release. They show up in stereo as small localized
slightly elevated areas on the surface. Figure 6 shows
the fan we believe may be actively venting."
HiRISE Views of the Sublimation of Mars’ Southern Seasonal CO2 Cap, p. 3.

In Fig. 1 of this report is also given color before and after images of a geyser region. The authors do not say these images are "false color" or "enhanced color", but it is interesting the changes appear blue in color.

Bob Clark