Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See page_maxonapi_getting_started_foundations_cinema_parameters.
Parameter: Vertex Colors
ID_VERTEXCOLOR_VERTEXCOLORMODE
Parameter: Display Alpha
ID_VERTEXCOLOR_ALPHAMODE
Parameter: Draw Points Always
ID_VERTEXCOLOR_DRAWPOINTS
Parameter: Use Transfer
ID_VERTEXCOLOR_USEFIELDS
Parameter: Transfer Mode
ID_VERTEXCOLOR_TRANSFER_MODE
Parameter: Use Deformed Points
ID_VERTEXCOLOR_USEDEFORMEDPOINTS
Parameter: Fields
ID_VERTEXCOLOR_FIELDS