title: Add new colors along with custom theme colors angular2 material
body: <p>how to add new colors in Angular 2 material.</p>
  
  <p>Its specified in the ng2-material docs: color: "primary"|"accent"|"warn" are accepted i want to add something like "progressbarcolor" other than the colors defined in my custom theme for angular2 material. </p>
  
  <p>For eg :</p>
  
  <pre><code> &lt;md-progress-bar color="progressbarcolor"&gt;    &lt;/md-progress-bar&gt;
  </code></pre>