“Dry ice has a much higher vapor pressure and evaporates even faster.”
Those ice caps aren’t fogging things up the way you see dry ice behave on earth. That’s how cold it is on the N pole of Mars. Maybe there’s frozen CO2 below the ice’s edge where it gets a little warmer during the day. When it starts to expand it has a heaving effect on the rocks sitting on top of it. Maybe that’s why you see more of a red cloud of dust than you would a white cloud of vapor.
Lots of maybes here. Just goes to show that science doesn’t have the answers. Only conjecture.