title: d3.js color range and lighter color range
body: <p>I would like to have two color ranges, the second one must consist off the same colors, but lighter.</p>
  
  <pre><code>rangeLength=10
  color = d3.scale.linear().domain([1,rangeLength]).range(['red', 'blue']);
  colorLigher= d3.scale.linear().domain([1,rangeLength]).range(['red'.lighter(10), 'blue'.lighter(10)]);
  </code></pre>
  
  <p>Obviously doesn't work, as 'red' is a string.</p>
  
  <p>Thanks in advance</p>