TeeChart : How to change marks format color at runtime ?

I'm using Delphi 10.3  upd with a Teechart component .

At run-time I need to put marks for specific points and customize the text and colors of these marks .   I've succeded in change texts using the following comands :

Chart1.[idxserie].Marks.Item[idxelement].Visible := True;
Chart1.[idxserie].Marks.Iidxelement]].Font.Color := clRed;
Chart1.[idxserie].Marks.item[idxelement]].Text.Add('My text is here');

now  I need to change the color of the line that links the text to the poin in the graph curve.  In design time, this property is located at  :

Editing chart window  : 

          Series -- myserie1 -

                    tab : Marks 

                               -- tab Arrows

                                             -- tab Border 

                                                         tab  -- Format     

                                                                     Button : Color 

How do I access and change the value of this property on run-time ? 

I've alreeady  tried :   

Chart1.[idxserie].Marks.Arrow.Color  := clRed                ==> nothing changed ! 

I appreciate your support.

This is where I change the property at design time :

This is what I want : the dotted line in red  and some of them in green,  (but only for some marks to be shownn during runtime)

Thanks.