Calling the OnDrawColumnCell procedure Delphi DBGrid

Question

I have DBGrid which stores client information and the expiry dates of memberships. I am using the following code on the OnDrawColumnCell event of the DBGrid to color rows which include memberships which are expiring (teal) or expired (red):

procedure TfrmMain.grdMainDrawColumnCell(Sender: TObject; const Rect: TRect;
  DataCol: Integer; Column: TColumn; State: TGridDrawState);
begin
  if (ADOMember.FieldByName('expirydate').AsDateTime >= (now)) and (ADOMember.FieldByName('expirydate').AsDateTime <= (now+7)) then
  begin
    grdMain.Canvas.Brush.Color := clTeal;
    grdMain.Canvas.Font.Color := clWhite;
    grdMain.DefaultDrawColumnCell(Rect, DataCol, Column, State);
  end;
  if (ADOMember.FieldByName('expirydate').AsDateTime < (now)) and (ADOMember.FieldByName('expirydate').AsString <> '') then
  begin
    grdMain.Canvas.Brush.Color := clRed;
    grdMain.Canvas.Font.Color := clWhite;
    grdMain.DefaultDrawColumnCell(Rect, DataCol, Column, State);
  end;
end; 

I also have a button on my form which resets the DBGrid. This allows a user to show the full list of clients after a search has been completed (returning a small number of clients).

My problem occurs when pressing the reset button. The button executes the following SQL function (within a procedure called ResetMemberGrid) correctly, as the full list is displayed.

SELECT * FROM customers

However, the DBGrid is not colored anymore. All the rows remain white. I have not been able to call the grdMainDrawColumnCell procedure, as it requires parameters which I am not aware of. Is there a way to call the DrawColumnCell procedure? I have tried to Repaint, Invalidate and Refresh the DBGrid, with no luck. Thanks.