title: Calculate color values from green to red
body: <p>I would like to calculate color value according to given number.</p>
  
  <pre><code>0 -&gt; pure red
  100 -&gt; pure green
  
  example: 75 -&gt; color, which is 75% from red to green.
  </code></pre>
  
  <p>I need this for expiration counter, which shows appropriate colors as days count down.</p>