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