trackBorderColor property
Color of the track border.
Defaults to Colors.transparent.
Widget build(BuildContext context) {
  return SfCartesianChart(
    series: <ColumnSeries<SalesData, num>>[
      ColumnSeries<SalesData, num>(
        isTrackVisible: true,
        trackBorderColor: Colors.red
      ),
    ],
  );
}
Implementation
final Color trackBorderColor;