Chart with positive range fills

HTML

<script src="http://www.amcharts.com/lib/amcharts.js" type="text/javascript"></script>
<div id="chartdiv" style="width: 100%; height: 340px;"></div>

CSS

body {
    font-size:12px;
    color:#000000;
    background-color:#ffffff;
    font-family:verdana, helvetica, arial, sans-serif;
}

JavaScript

var chart;
var chartData = [];
var chartCursor;

// generate some random data
function generateChartData() {
    var firstDate = new Date();
    var temperature = 29;
    firstDate = addMinutes(firstDate, -20);

    chartData.push({ date: addMinutes(firstDate, -7), visits: 29.5, baseline: 29.5 });
    chartData.push({ date: addMinutes(firstDate, -6), visits: 29.5, baseline: 29.5 });
    chartData.push({ date: addMinutes(firstDate, -5), visits: 30.5, baseline: 30.5 });
    chartData.push({ date: addMinutes(firstDate, -4), visits: 29.5, baseline: 29.5 });
    chartData.push({ date: addMinutes(firstDate, -3), visits: 28.5, baseline: 28.5 });
    chartData.push({ date: addMinutes(firstDate, -2), visits: 27.5, baseline: 28 });
    chartData.push({ date: addMinutes(firstDate, -1), visits: 28.5, baseline: 28.5 });
    chartData.push({ date: firstDate, visits: 29.5, baseline: 29.5 });
}

function addMinutes(date, minutes) {
    return new Date(date.getTime() + minutes*60000);
}

function varyTemperature(temperature) {
	var min = -0.2;
	var max = 0.2;
	var random = Math.random() * (max - min) + min;
    return temperature + random;
}

// create chart
AmCharts.ready(function () {
    // generate some data first
    generateChartData();

    // SERIAL CHART    
    chart = new AmCharts.AmSerialChart();
    chart.pathToImages = "http://www.amcharts.com/lib/images/";
    chart.marginTop = 0;
    chart.marginRight = 10;
    chart.autoMarginOffset = 5;
    chart.zoomOutButton = {
        backgroundColor: '#000000',
        backgroundAlpha: 0.15
    };
    chart.dataProvider = chartData;
    chart.categoryField = "date";

    // AXES
    // category
    var categoryAxis = chart.categoryAxis;
    categoryAxis.parseDates = true; // as our data is date-based, we set parseDates to true
    categoryAxis.minPeriod = "mm"; // our data is in minutes, so we set minPeriod to mm
    categoryAxis.dashLength = 1;
    categoryAxis.gridAlpha = 0.15;
    categoryAxis.axisColor = "#DADADA";
   ...