[Solved]-Change data hover line color in Highcharts-Highcharts

you can change tooltip.crosshairs options to change the width, color, dashstyle and zindex of the line. here's the code for width and color:

tooltip: {
    crosshairs: [{
            width: 3,
            color: 'green'
    }]
}

the first object of the array is for the xaxis, the second for the yaxis. here's the demo.