A report to be presented at the 34th Lunar and Planetary Science Conference will discuss color imaging using the THEMIS instrument on Mars Odyssey:

Color Imaging of Mars with the Visible Imaging Subsytem (VIS) on the Mars Odyssey THEMIS Instrument.
J.F. Bell III1, T. McConnochie, M.J. Wolff, P.R. Christensen3, G. Mehall, M. Malin, M. Caplinger4, M. Ravine,
L.L. Cherednik, K.C. Bender, K. Murray, and the THEMIS Science Team.
Lunar and Planetary Science XXXIV (2003) 1993.pdf
http://www.lpi.usra.edu/meetings/lpsc2003/pdf/1993.pdf

One of the images discussed in this report, of Candor Chasma, was already released and appears to show greenish areas in the image:

From: Robert Clark (rgregoryclark@yahoo.com)
Subject: Mars, the "Greenish" Planet?
Newsgroups: sci.astro, alt.sci.planetary, sci.space.history, sci.astro.amateur, rec.arts.sf.science
Date: 2002-12-11 18:31:56 PST
http://groups.google.com/groups?th=4a3ea56991ef1f46

However, the other image is a new color one of Syrtis Major and appears to show blue deposits in the craters. Syrtis Major has long been known to present a phenomemon of a "blue clearing" that changes seasonally. For this reason, it was attributed by some to vegetation. Others attributed it to variable dust cover:

From: Robert Clark (rgregoryclark@yahoo.com)
Subject: On the colors of Mars and the mystery of the "Sinton bands".
Newsgroups: sci.astro, alt.sci.planetary, sci.astro.seti, sci.bio.misc
Date: 2002-02-02 15:19:44 PST
http://groups.google.com/groups?th=6e501f3d9d0901c9

The LPSC report notes the difficulty of calibrating and combining the different THEMIS band images into a single visible color image. One thing that might help is to use images where you can be sure of some of the colors, for example by using images that contain clouds or ice that you can assume are white:

Clouds in the Northern Tempe Terra (Released 2 May 2002)
http://themis.la.asu.edu/zoom-20020502a.html

Hungarian Scientists Claim to Have Found Traces of Life on Mars.
By Krisztina Than
Reuters
posted: 12:00 pm ET
07 September 2001
"The three-man team said the pictures showed evidence of thousands of dark dune spots, similar to organisms found near Earth's South Pole, in craters in Mars' snowy southern polar region.
"These spots indicate that on the surface below the ice there are such organisms which, absorbing solar energy, are able to melt the ice and create conditions of life for themselves,'' biologist and team member Tibor Ganti told Reuters."
http://www.space.com/scienceastronomy/mars_organisms_010907.html

Latest Claims Of Martian Life Are Erroneous Says USGS Scientist.
Flagstaff - Sept. 26, 2001
by Timothy N. Titus, Ph.D
U.S.G.S. Astrogeology Team
"Hungarian scientists have reported evidence of life in the Martian southern polar region. They claim that the dark spots observed during the southern spring are living organisms, similar to those found at the south pole of Earth.
"This comparison of the Martian southern polar cap to the Earth's Antarctica is highly inaccurate and misleading since the two regions have little in common."
http://www.spacedaily.com/news/mars-life-01h.html

Color images of these south pole dark spots may help to resolve the controversy as to whether or not they are related to life.

Bob Clark