I just finished adding support to output color volumes. The changes will be in the next daily build (14.0.349).
Similar to the other volumes (density, temperature, fuel, vel), the Cd. volumes are mapped to the color grid of the fluidShape node. So if your Houdini asset outputs volumes “density” and "Cd.", then they will all be mapped to one fluid shape in Maya.
Note that in order for the volumes to be mapped, the resolutions of the volumes (Cd, density, etc.) have to match, because Maya requires that all the grids of a fluid shape to have the same resolution.
Attached a sample asset to demonstrate color output. Enjoy!