Losing table rulings when setting cell.CellUseOverrideShading = true; How do I keep existing table rulings?

Hi All,

I am applying a custom shading to a cell, according to an attribute setting, however after the custom shading is applied,  I lose the table rulings that were present. How do I tell it in code to keep existing rulings?

cell.CellUseOverrideShading = true ;

                cell.CellUseOverrideFill = true ;

                cell.CellOverrideFill = 0 ; // change the table

                var colorObj = doc.GetNamedColor("MYshading");

                cell.CellOverrideShading = colorObj;

thanks,

Tracey