title: Drawing a pie chart in gray scale using matplolib of python
body: <p>I try to draw a pie chart in grayscale using matplolib of python.
  But what I have is grayscale data of color which are vary between 0 and 255
  Using these grayscale data, can I draw gray scale pie chart?</p>
  <pre><code>data = [10,20,30]
  colors = [20, 100, 150] # grayscale data
  plt.pie(data, colors = colors)
  </code></pre>