x-circle and r-circle Smith Chart color

Hi,
I would like to customize the color of the Smith Chart, but I do not know which attribute I should modify ?
With the default setting colors, the x-circle and r-circle of the Smith Chart are plotted in blue. I would like to change these default colors to a specified color, wich I can modify by programing.
In other words, I would like to know which atributes of the graph which I should modify to set a specific color?( means the attribute to put in SetCtrlAttribute function to modify the x-cricle and r-circle colors of the Smtih Chart).

The background of this smith Chart is modified with ATTR_PLOT_BGCOLOR attribute, in which the default value is the gray. The ATTR_PLOT_BGCOLOR is attribute of a classical Graph, as the smith chart is obtained by converting this classical graph.
Thank you so much for your answer.
Best regards,
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hapiest