title: Change line chart area color in Angular-NVD3
body: <p>I'm using the Angular-NVD3 library to show some line charts, I've seen that I can set an "area" property to 'true' in the data so that the area of the graph will be colored. </p>
  
  <pre><code>{
      values: [/** some data **/],
      key: 'Cosine Wave',
      color: '#2ca02c',
      area: true
  }
  </code></pre>
  
  <p><a href="http://plnkr.co/edit/lXV7rNpNGBpYWeDh7JPI?p=preview" rel="nofollow noreferrer">live example</a></p>
  
  <p>but I cannot find how to change the color of the area. by default the chart colors the area to a lighter hue of the line color, but I need it as a light gray.</p>
  
  <p>Does the API ($scope.options) even allow for such an option? is there a way to 'hack' it ?</p>