indexLabelBorderColor: String

Sets the Border color of Index Labels. The value of indexLabelBorderColor can be a “HTML Color Name”, “hex code”, or “rgba values”.

var  chart =  new  CanvasJS.Chart("container", {
 .
 .
 data: [{
    indexLabelBorderColor: "red",
    indexLabelBorderThickness: 1
 }]
 .
 . 
});
chart.render();