title: How to make Canvas widget color darker compared to the original color?
body: <p>I have this canvas widget with a green rectangle:</p>
  
  <pre><code>canvas = tk.Canvas(root)
  canvas.create_rectangle(0,0,50,100, fill='green')
  </code></pre>
  
  <p>I want to darken it. So:</p>
  
  <pre><code>canvas.itemconfig(1, fill=?????)
  </code></pre>
  
  <p>The issue is, what should I put in the <code>?????</code> aka the 'darker' color of the original color.</p>
  
  <p>Sure, I can just find a hex for a darker shade of green or something like that, but the point is: <strong>How can I find the darkened the widget based on the original color?</strong></p>
  
  <p>I don't necessarily need to find the darker version of the color if there is something like: <code>canvas.itemconfig(1, darkness=-100)</code>.</p>