[Solved]-Highcharts: Style Zero Y value-Highcharts

take a look at the plotlines api in the yaxis...

http://api.highcharts.com/highcharts#yaxis.plotlines

example... http://jsfiddle.net/48dul/

$(function () {
var chart = new highcharts.chart({
    chart: {
        renderto: 'container'
    },
    xaxis: { 
        categories: ['jan', 'feb', 'mar', 'apr', 'may', 'jun', 'jul', 'aug', 'sep', 'oct', 'nov', 'dec'],
    },
            yaxis: { 
        plotlines: [{
            color: '#c0c0c0',
            width: 5,
            value: 0
        }]
    },

    series: [{
        data: [-29.9, -71.5, -106.4, -129.2, 144.0, 176.0, 135.6, 148.5, 216.4, 194.1, 95.6, 54.4]
    }]
});

});