Mars ***is*** the furthest rocky planet, before the first gas giant. Its iron core cooled off and solidified long ago, dropping the planet's magnetic field, and thus exposing it to the full force of the solar wind. That stripped away its atmosphere over a very long time. Hence, no water. There is ice you can see with a telescope, but it's CO2 dry ice at the poles. The red color is just the composition of the remaining rock. This is still only theory, but it's the reason NASA is continually hunting clues that water once existed there. But even comets made mostly from water ice don't appear white. The Rosetta mission surprisingly found its target comet to be very dark in color. I think a better question would be: If the Traveler terraformed Mars, why is it *still* a desert unlike Venus, why does it have Earth's gravity, and how long until this atmosphere bleeds off like the last one?