Problem selecting a single cell in a tablegrid

I have a TableGrid it has  5 columns.  Column 5 has a checkbox enabled by selecting checkbox under 'settings'.

My intention is to click in cell 5 on a specific row and cause the current date to be entered into cell 4. I then want to change the font color of the row.

I have the code below  which partly works, the checkbox appears and the date does get entered into the correct cell.

However, I can click anywhere on the row to get this to happen, what I want is to have just column 5 cell to perform the date function when clicked.

I can't get the row font colour to change at all, though I would be just as happy to have a row grayed out.

procedure frmMain_grdOrders_OnCellClick (Sender: TObject; ACol, ARow: Integer);
 var
     YY,MM,DD:Word;

begin
    DecodeDate(frmMain.DateTimePicker1.DateTime,YY,MM,DD); //get only the date portion of datetime

    if frmMain.grdOrders.Cell[5,ARow].Empty = false then    //checkbox is unticked
    begin
        frmMain.grdOrders.Cell[4,ARow].AsDateTime := EncodeDate(YY,MM,DD); 
        frmMain.grdOrders.font.color:= clGreen;

    end;  
 

       
end;

Any ideas greatfully received.