title: change colour of individual bar in bar graph using c3js
body: <p>How to change the color of individual bar in a bar graph.</p>
  
  <pre><code>    var chart = c3.generate({
      data: {
          columns: [
              ['data1', 30, 20, 50, 40, 60, 50]
  
          ],
          type: 'bar',
          colors: {
              data1: '#ff0000'
          },
          color: function (color, d) {
  
              return d.id &amp;&amp; d.id === 'data1' ? d3.rgb(color).darker(d.value / 120) : color;
          }
      }
  });
  </code></pre>
  
  <p>Here, all bars which have value greater than 45 should be green in color and those below 45 should be red in color.</p>