A feature to solve this without "hacks" was added in Highcharts 4.1.0 (February 2015), called zones (API). The given problem can be solved like this, using zones:
plotOptions: {
series: {
zones: [{
value: 0, // Values up to 0 (not including) ...
color: 'blue' // ... have the color blue
},{
value: 10, // Values up to 10 (not including) ...
color: 'orange' // ... have the color orange
},{
color: 'red' // Values from 10 (including) and up have the color red
}]
}
}
See this JSFiddle demonstration of how it looks.