Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See Parameter IDs.
Parameter: Vertex Colors
ID_VERTEXCOLOR_VERTEXCOLORMODEParameter: Display Alpha
ID_VERTEXCOLOR_ALPHAMODEParameter: Draw Points Always
ID_VERTEXCOLOR_DRAWPOINTSParameter: Use Fields
ID_VERTEXCOLOR_USEFIELDSParameter: Use Deformed Points
ID_VERTEXCOLOR_USEDEFORMEDPOINTSParameter: Fields
ID_VERTEXCOLOR_FIELDS