jquery直接找到那條線設置顏色
$('#container').highcharts({/*你的配置*/});
var grid = $('div.highcharts-grid'), vml = false;
if (grid.length == 0) grid = $('g.highcharts-grid');
else vml = true;
line = grid.find(vml ? 'shape' : 'path').eq(4);
if (vml) line.css('background-color', 'red');
else line.attr('stroke', '#ff0000');