score:2

Accepted answer

creating my own jsfiddle to work with, it appears the configuration usehtml is case-sensitive and changing usehtml to usehtml correctly creates δ in the categories

highcharts.chart('container', {

  chart: {
    type: 'bar'
  },

  title: {
    text: 'catawba average points'
  },

  xaxis: {
    categories: ['emergency ts δs', 'column b', 'column c', 'column d', 'column e', 'column f', 'column g'],
    labels: {
      usehtml: true
    }
  },

  plotoptions: {
    bar: {
      stacking: 'normal',
      grouppadding: 0.10,
      pointpadding: 0,
      datalabels: {
        enabled: true,
        alignt: 'right',
        formatter: function() {
          if (this.y != 0) {
            return this.y;
          }
        }
      }
    }
  },

  series: [{
    name: '(-) var',
    data: [0, 0, 0, 0, 0, 2, 0, 0],
    color: '#ffa6a6',
    stack: '2017q3',
    showinlegend: false
  }, {
    name: '(+) var',
    data: [0, 0, 0, 0, .1, 0, 0, 5.10],
    color: '#a6e3c2',
    stack: '2017q2',
    showinlegend: false
  }, {
    name: '2017q3',
    color: '#d9d9d9',
    data: [10, 15, 10, 10, 3.1, 0, 25, 15],
    stack: '2017q3'
  }, {
    name: '2017q2',
    color: '#f2f2f2',
    data: [10, 15, 10, 10, 3.0, 2, 25, 9.90],
    stack: '2017q2'
  }]


});
<script src="https://code.highcharts.com/highcharts.js"></script>


<div id="container" style="min-width: 310px; height: 600px; margin: 0 auto"></div>

score:1

you could try the unicode representation as \u0394. this appears to work with labels.usehtml: true.

highcharts.chart('container', {

  chart: {
    type: 'bar'
  },

  title: {
    text: 'catawba average points'
  },

  xaxis: {
    categories: ['emergency ts \u0394s', 'column b', 'column c', 'column d', 'column e', 'column f', 'column g'],
    labels: {usehtml: true}
  },

  plotoptions: {
    bar: {
      stacking: 'normal',
      grouppadding: 0.10,
      pointpadding: 0,
      datalabels: {
        enabled: true,
        alignt: 'right',
        formatter: function(){
        if(this.y != 0){
         return this.y;
        }
        }
      }
    }
  },

  series: [{
    name: '(-) var',
    data: [0, 0, 0, 0, 0, 2, 0, 0],
    color: '#ffa6a6',
    stack: '2017q3'
  }, {
    name: '(+) var',
    data: [0, 0, 0, 0, .1, 0, 0, 5.10],
    color: '#a6e3c2',
    stack: '2017q2'
  }, {
    name: '2017q3',
    color: '#d9d9d9',
    data: [10, 15, 10, 10, 3.1, 0, 25, 15],
    stack: '2017q3'
  }, {
    name: '2017q2',
    color: '#f2f2f2',
    data: [10, 15, 10, 10, 3.0, 2, 25, 9.90],
    stack: '2017q2'
  }]


});

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