EmberCharts - Cannot read 'color' of undefined

I am trying to render a simple vertical bar chart using the Ember Charts add on but I can't get it to render on the page. I have been following the tutorial provided here with no luck.

\\ dashboard.hbs
<div class="chart-container">

<h1>text</h1>
</div>

\\ dashboard.js (controller)
import Controller from '@ember/controller';

export default Controller.extend({
    ajax: Ember.inject.service(),

    init: function() {
   this._super;
   this.get('ajax')
     .request('barchart').then((data)=>{
       this.set('bardata', data);

   })
 }

});

\\ ajax.js (service)
import Service from '@ember/service';
import Ember from 'ember';
import AjaxService from 'ember-ajax/services/ajax';

export default AjaxService.extend({
  host:
   'http://server:port/api'
});

When I load the route there is an empty space where I would expect the chart to be.

When I investigate the Network developer tools I can see that the 'barchart' data is succesfully retrieved in the following format:

[
{"value":74,"label":"2017-12-20"},
{"value":16,"label":"2017-12-21"}
]

where value is an integer and label is varchar which seems to be correct as per the documentation.

Console produces the following error:

Uncaught TypeError: Cannot read property 'color' of undefined
    at colorable.js:89
    at vertical-bar-chart.js:412
    at Array.forEach (<anonymous>)
    at Class.<anonymous> (vertical-bar-chart.js:411)
    at ComputedPropertyPrototype.get (ember-metal.js:3252)
    at get (ember-metal.js:2594)
    at Class.get (observable.js:37)
    at Class.<anonymous> (vertical-bar-chart.js:441)
    at ComputedPropertyPrototype.get (ember-metal.js:3252)
    at get (ember-metal.js:2594)

I tried adding a manual selectedSeedColor but there was no change in the response.