title: Chart.js Line, different fill color for negative point
body: <p>I need to change the fill color (internal area) in a Line Chart.js when the point is negative.</p>
  
  <p>The code is simple and basic:</p>
  
  <pre><code>$(document).ready(function(){
  
    var ctx = $("#myChart").get(0).getContext("2d");
  
    var data = {
        labels: ["January", "February", "March", "April", "May", "June", "July"],
        datasets: [
            {
                label: "My First dataset",
                //fillColor : "rgba(60,91,87,1)",
                // String - the color to fill the area under the line with if fill is true
                backgroundColor: "rgba(75,192,192,0.4)",
                strokeColor : "rgba(60,91,87,1)",
                pointColor : "rgba(60,91,87,1)",
                pointStrokeColor : "#58606d",
                // The actual data
                data: [65, 59, 80, -81, 56, 55, -40],
  
                // String - If specified, binds the dataset to a certain y-axis. If not specified, the first y-axis is used. First id is y-axis-0
                yAxisID: "y-axis-0",
            }
        ]
    };
  
    var options = {
        scales: {
            yAxes: [{
                display: true,
                ticks: {
                    suggestedMin: 0,    // minimum will be 0, unless there is a lower value.
                    // OR //
                    beginAtZero: true   // minimum value will be 0.
                }
            }]
        }
    };
  
    var myLineChart = new Chart(ctx, {
        type: 'line',
        data: data,
        options: options
    });
  
  //  myLineChart.data.datasets[0].metaDataset._points[3]._model.backgroundColor = "red";
  //  if (myLineChart.datasets[0].points[4].value &lt; 0) {
  //    myLineChart.datasets[0].points[4].fillColor =  "red";
  //    myLineChart.update();
  // }
  })
  </code></pre>
  
  <p>I'm trying to get this result:</p>
  
  <p><a href="https://i.stack.imgur.com/ZQMR3.png" rel="noreferrer"><img src="https://i.stack.imgur.com/ZQMR3.png" alt="enter image description here"></a></p>