title: spline chart highchart to fill the color in series
body: <p>I have created one highchart in <a href="https://jsfiddle.net/d8rL0kyp/1/" rel="nofollow noreferrer">jsfiddle</a></p>
  
  <p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
  <div class="snippet-code">
  <pre class="snippet-code-js lang-js prettyprint-override"><code>Highcharts.chart('container', {
    chart: {
      type: 'areaspline',
  
  
    },
    title: {
      text: 'Soverign Capped 1 year PD',
      align: 'left',
      backgroundColor: 'gray',
      style: {
  
        fontSize: "12px",
  
      }
    },
    subtitle: {
      text: '30 days moving average',
      align: 'left',
      style: {
        color: 'gray',
        fontSize: "8px",
  
  
      }
    },
  
  
    xAxis: {
      categories: [
        '10/11/2019',
        '11/11/2019',
        '12/11/2019',
        '1/11/2020',
        '2/11/2020',
        '3/11/2020',
        '4/11/2020'
  
      ],
      min: 0.5,
      max: 5.5,
      startOnTick: false,
      endOnTick: false
  
    },
    yAxis: {
      title: {
        text: 'PD%',
        align: 'high',
        fontWeight: 'bold'
      },
  
  
  
      max: 25,
      startOnTick: false,
      endOnTick: false
    },
    tooltip: {
      enabled: false
    },
    credits: {
      enabled: false
    },
    plotOptions: {
      series: {
        marker: {
          enabled: false
        },
        states: {
          inactive: {
            opacity: 1
          }
        },
        dataLabels: {
          enabled: true,
          inside: true,
          style: {
            fontWeight: "bold",
          },
          formatter: function() {
            if (this.x == "4/11/2020") {
              return this.series.name;
            }
          }
  
        }
  
      },
      enableMouseTracking: false,
      tooltip: {
        enabled: false
      },
      areaspline: {
        fillOpacity: 1,
      },
  
  
    },
  
    series: [{
        color: '#fbb189',
        name: 'Deitrioting',
        showInLegend: false,
        data: [25, 25, 25, 25, 25, 25, 25]
      },
      {
        color: '#fff2d0',
        name: 'Stable',
        showInLegend: false,
        data: [3, 4, 5, 5, 4, 10, 10]
  
  
      }, {
        color: '#c2e0b7',
        name: 'Improving',
        showInLegend: false,
        data: [1, 3, 4, 3, 3, 5, 7]
      },
      {
        name: '',
        showInLegend: false,
        type: 'spline',
        data: [7.0, 6.9, 9.5, 12, 23, 4, 3]
      }
    ]
  });</code></pre>
  <pre class="snippet-code-html lang-html prettyprint-override"><code>&lt;script src="https://code.highcharts.com/highcharts.js"&gt;&lt;/script&gt;
  &lt;div id="container"&gt;&lt;/div&gt;</code></pre>
  </div>
  </div>
  </p>
  
  <p>Currently, I have defined different colour for the different series. But for the last date, I want to set the red colour for all the series.</p>
  
  <p>Can you help me with this?</p>
  
  <p>Sample image attached below.</p>
  
  <p><a href="https://i.stack.imgur.com/joS01.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/joS01.png" alt="enter image description here"></a></p>