HighCharts : Is it possible to customize the colors of individual series?

Options can be set separately for each series.

var chart = new Highcharts.Chart({
    chart: {
        renderTo: 'container'
    },
    xAxis: {
        type: 'datetime'
    },

    series: [{
        name: 'John',
        color: '#0066FF',
        dashStyle: 'ShortDash',
        data: [
            [Date.UTC(2010, 0, 1), 29.9],
            [Date.UTC(2010, 2, 1), 71.5],
            [Date.UTC(2010, 3, 1), 106.4]
        ]
    },{
        name: 'Mary',
        color: '#FF0000',
        data: [
            [Date.UTC(2010, 0, 1), 60.9],
            [Date.UTC(2010, 1, 1), 40.5],
            [Date.UTC(2010, 2, 1), 90.0],
            [Date.UTC(2010, 3, 1), 80.4]
        ]
    }]
});

JsFiddle Example