title: How to calculate color shadows codes?
body: <p>I would like to know / calculate color codes of N red shadows (N can be 5, 20, or 50, for example).</p>
  
  <p>How could I do this ?</p>
  
  <p>I noticed, for example, that the following gives some red shadows:</p>
  
  <ul>
  <li>R = 255, G = B = 0..255</li>
  <li>R = 0..255, G = B = 0</li>
  </ul>
  
  <p>Is there any known method to calculate shadows ?</p>