indexLabelBorderColor: String

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

var  chart =  new  CanvasJS.Chart("container", {
 .
 .
 data: [{
    dataPoints:[
        { y: 10, indexLabelBorderColor: "red", indexLabelBorderThickness: 1 },
        .
        .
    ]
 }]
 .
 . 
});
chart.render();