Liquid CO2
Is clear, like water. Not even that hint of blue.
Liquid CO2 won't hang around on the surface of Mars, it explodes.
(So all the channels must be formed by gas and debris clouds, in a CO2-based interpretation)
I magine something so much larger than the grand canyon with a howling storm of boiling CO2 gas, dust, sand, and rocks pouring down it at Mach 0.5...