Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See Parameter IDs.
Parameter: Function
GV_COLORSPACE_FUNCTION_IDParameter: Hue from 0.0 to 360.0
GV_COLORSPACE_HUE360Parameter: RGB from 0 to 255
GV_COLORSPACE_RGB255Parameter: Input
GV_COLORSPACE_INPUTParameter: Output
GV_COLORSPACE_OUTPUT