connectorLineColor property
Color of the selection zooming tooltip connector line.
late ZoomPanBehavior zoomPanBehavior;
void initState() {
  zoomPanBehavior = ZoomPanBehavior(
    enableSelectionZooming: true,
  );
  super.initState();
}
Widget build(BuildContext context) {
  return SfCartesianChart(
    zoomPanBehavior: zoomPanBehavior,
    primaryXAxis: NumericAxis(
      interactiveTooltip: InteractiveTooltip(
        connectorLineColor: Colors.red
      )
    ),
  );
}
Implementation
final Color? connectorLineColor;