conditional marker colors in highcharts

I'm using Highcharts and I want to fill markers in line chart with different colors. For example: when variable "a" is 1 then fill marker with red else fill with green. Is it possible to do that? Here is the code: http://jsfiddle.net/EnyCJ/1/ I was trying to do that with formatter but it doesn't work. Any suggestions? ``` var a=1; plotOptions: { series: { marker: { fillColor: { formatter: function () { if (a == 1) { return 'red' } else { return 'green' } } }, lineWidth: 2, } } }, ```