title: C3.js add color to an horizontal line
body: <p>Is there a way in C3.js for to add COLOR to an horizontal line, the level 0 in axis y in bar graphs? By default you have this graph:</p>
  
  <p><a href="https://i.stack.imgur.com/cGM5m.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/cGM5m.png" alt="enter image description here"></a></p>
  
  <p>What I need is this:</p>
  
  <p><a href="https://i.stack.imgur.com/7F7G3.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/7F7G3.png" alt="enter image description here"></a></p>
  
  <p>Any idea? thanks.</p>
  
  <p>UPDATE: I've made a line with this, but I need to add color.</p>
  
  <pre><code>grid: {
              y: {
                  lines: [
                      {value: 0, text: ''}
                  ]
              }
          }
  </code></pre>