public class SegmentSymbolOptions 

/// <summary>
/// Within the specialization of a MapTool, this method handles activation and deactivation of the tool, allowing customization of sketch segment and vertex symbology when
/// the tool becomes active.  When the tool is activated, this method customizes the appearance of sketch segments and vertices by updating their symbol options. This includes setting colors, widths, marker types, and other visual properties for both segments and regular unselected vertices.
/// </summary>
protected override Task OnToolActivateAsync(bool active)
{
  QueuedTask.Run(() =>
  {
    //Getting the current symbology options of the segment
    var segmentOptions = GetSketchSegmentSymbolOptions();
    //Modifying the primary and secondary color and the width of the segment symbology options
    var deepPurple = new CIMRGBColor() { R = 75, G = 0, B = 110 };
    segmentOptions.PrimaryColor = deepPurple;
    segmentOptions.Width = 4;
    segmentOptions.HasSecondaryColor = true;
    var pink = new CIMRGBColor() { R = 219, G = 48, B = 130 };
    segmentOptions.SecondaryColor = pink;
    //Creating a new vertex symbol options instance with the values you want
    var vertexOptions = new VertexSymbolOptions(VertexSymbolType.RegularUnselected);
    var yellow = new CIMRGBColor() { R = 255, G = 215, B = 0 };
    var purple = new CIMRGBColor() { R = 148, G = 0, B = 211 };
    vertexOptions.AngleRotation = 45;
    vertexOptions.Color = yellow;
    vertexOptions.MarkerType = VertexMarkerType.Star;
    vertexOptions.OutlineColor = purple;
    vertexOptions.OutlineWidth = 3;
    vertexOptions.Size = 5;

    //Setting the value of the segment symbol options
    SetSketchSegmentSymbolOptions(segmentOptions);
    //Setting the value of the vertex symbol options of the regular unselected vertices using the vertexOptions instance created above.
    SetSketchVertexSymbolOptions(VertexSymbolType.RegularUnselected, vertexOptions);
  });

  return base.OnToolActivateAsync(active);
}

{
  var options = ApplicationOptions.EditingOptions;

  //var options = ApplicationOptions.EditingOptions;
  await QueuedTask.Run(() =>
  {
    var seg_options = options.GetSegmentSymbolOptions();
    //to convert the options to a symbol use
    //SymbolFactory. Note: this is approximate....sketch isn't using the
    //CIM directly for segments
    var layers = new List<CIMSymbolLayer>();
    var stroke0 = SymbolFactory.Instance.ConstructStroke(seg_options.PrimaryColor,
      seg_options.Width, SimpleLineStyle.Dash);
    layers.Add(stroke0);
    if (seg_options.HasSecondaryColor)
    {
      var stroke1 = SymbolFactory.Instance.ConstructStroke(
        seg_options.SecondaryColor, seg_options.Width, SimpleLineStyle.Solid);
      layers.Add(stroke1);
    }
    //segment symbology only
    var sketch_line = new CIMLineSymbol()
    {
      SymbolLayers = layers.ToArray()
    };
  });
}

{
  var options = ApplicationOptions.EditingOptions;
  //var options = ApplicationOptions.EditingOptions;
  await QueuedTask.Run(() =>
  {
    //change the segment symbol primary color to green and
    //width to 1 pt
    var segSymbol = options.GetSegmentSymbolOptions();
    segSymbol.PrimaryColor = ColorFactory.Instance.GreenRGB;
    segSymbol.Width = 1;

    //Are these valid?
    if (options.CanSetSegmentSymbolOptions(segSymbol))
    {
      //apply them
      options.SetSegmentSymbolOptions(segSymbol);
    }
  });
}

{
  var options = ApplicationOptions.EditingOptions;
  //var options = ApplicationOptions.EditingOptions;
  await QueuedTask.Run(() =>
  {
    var def_seg = options.GetDefaultSegmentSymbolOptions();
    options.SetSegmentSymbolOptions(def_seg);
  });
}