Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See page_maxonapi_getting_started_foundations_cinema_parameters.
Parameter: Index
GV_VERTEXCOLORMAP_INPUT_INDEX
Parameter: Color
GV_VERTEXCOLORMAP_INPUT_VALUE_COLOR
Parameter: Alpha
GV_VERTEXCOLORMAP_INPUT_VALUE_ALPHA
Parameter: Color
GV_VERTEXCOLORMAP_OUTPUT_VALUE_COLOR
Parameter: Alpha
GV_VERTEXCOLORMAP_OUTPUT_VALUE_ALPHA
Parameter: Count
GV_VERTEXCOLORMAP_OUTPUT_COUNT