Components for Delphi and C++ Builder.

var
  s: String;
  CheckColumn: TColumnEh;
begin
  DBGridEh1.DefaultDrawColumnDataCell(Cell, AreaCell, Column, ARect, Params);
  CheckColumn := DBGridEh1.FieldColumns['NAME'];
  DBGridEh1.FieldColumns['NAME'].HideDuplicates := true;

  s := CheckColumn.DisplayText;
  if not DBGridEh1.CheckColumnDuplicateValues(CheckColumn, Params.Row, s, false) then
  begin
    DBGridEh1.Canvas.Pen.Color := clTeal;
    DBGridEh1.Canvas.Polyline([Point(ARect.Left, ARect.Bottom),
                               Point(ARect.Right+1, ARect.Bottom)]);
    DBGridEh1.Canvas.Polyline([Point(ARect.Left, ARect.Bottom-1),
                               Point(ARect.Right+1, ARect.Bottom-1)]);
  end;
  Processed := true;
end;