[Solved]-Is is possible to change line color in highchart xy plot for specific y range only?-Highcharts

The easiest way would be to separate the data and create separate series (with different colors) for the different ranges. That would mean, of course, that you would have to create a custom legend.

Edit to your function:

$(function () {
    var chart = new Highcharts.Chart({
        chart: {
            renderTo: 'container',
            zoomType: 'xy',
            type : 'scatter',
            marginLeft: 50,
            marginBottom: 90
        },

        yAxis: {
            reversed: true,

        },
        plotOptions: {
            series: {
                      animation: {
                                   duration: 2000
                                 },
                      lineWidth: 2
                    },
        },
        xAxis: {
            opposite: true  
        },
        series: [{
            name: 'Test Plot',
            data: [
                [28, 0],
                [29,1],
                [30, 3],
                [34, 4],
                [32,5],
                [28, 6]
            ],
            color: "#F90B0B"
        },
               {
            name: 'Test Plot2',
            data: [
                [28, 6],
                [24, 7],
                [19,8],
                [15, 9]
            ],
                   color: "#F909F9"
        }]
    });
});