Highcharts - solid gauge - solid color (no gradient)

HTML

<script src="http://code.highcharts.com/highcharts.js"></script>
<script src="http://code.highcharts.com/highcharts-more.js"></script>
<script src="http://code.highcharts.com/modules/solid-gauge.src.js"></script>

<div id="container-speed" style="width: 300px; height: 200px; float: left"></div>

JavaScript

$(function () {
	
    var gaugeOptions = {
	
	    chart: {
	        type: 'solidgauge'
	    },
	    
	    title: null,
	    
	    pane: {
	    	center: ['50%', '85%'],
	    	size: '140%',
	        startAngle: -90,
	        endAngle: 90,
            background: {
                backgroundColor: (Highcharts.theme && Highcharts.theme.background2) || '#EEE',
                innerRadius: '60%',
                outerRadius: '100%',
                shape: 'arc'
            }
	    },

	    tooltip: {
	    	enabled: false
	    },
	       
	    // the value axis
	    yAxis: {
			minColor: '#00FF00',
			maxColor: '#8c4848',
			lineWidth: 0,
            minorTickInterval: null,
            tickPixelInterval: 400,
            tickWidth: 0,
	        title: {
                y: -70
	        },
            labels: {
                y: 16
            }        
	    },
        
        plotOptions: {
            solidgauge: {
                dataLabels: {
                    y: -30,
                    borderWidth: 0,
                    useHTML: true
                }
            }
        }
    };
    
    upRandom = function(){
        var newGuageValue = Math.random() * 100;
        var chart = Highcharts.charts[0];
        var point = chart.series[0].points[0];
        var color = newGuageValue >= 80 ? [255,0,0,1] : (newGuageValue >= 60 ? [255,255,0,1] : [0,255,0,1]);
    chart.yAxis[0].stops[0].color.rgba = color;
    chart.yAxis[0].stops[1].color.rgba = color;
    point.update(newGuageValue);
       
        setTimeout(upRandom,1000);
    }
    
    // The speed gauge
    $('#container-speed').highcharts(Highcharts.merge(gaugeOptions, {
    	yAxis: {
	        min: 0,
	        max: 100,
	        title: {
	            text: ''
	        }       
	    },

	    credits: {
	    	enabled: false
	    },
	
	    series: [{
	        name: 'Speed',
	        data: [null],	        
	        tooltip: {
	            valueSuffix: ' km/h'
	        }
	    }]
	
    }), function(chart){
      ...