title: How to know if a tree is colorable
body: <p>I cannot understand why the following RB tree is not colorable.
  <img src="https://i.stack.imgur.com/B7HP9.jpg" alt="RBtree"></p>
  
  <p>I thought the only requirement was:</p>
  
  <blockquote>
    <p>The path from the root to the farthest leaf is no more than twice as long as the path from the root to the nearest leaf.</p>
  </blockquote>
  
  <p>But in the image you can see the shortest path (orange) is 2 and the longest path (blue) is 4, which means it should be colorable according to the rule above.</p>