title: How to color different cells based on the value of the cells in a Python pandas DataFrame
body: <p>I have a pandas DataFrame with different string values to be filled by different colors.
  For the following DataFrame <code>df</code>, all I want is that different cells are in different colors. For example, the cells that have 'A' value is in red, the cells that have 'B' value is in green, and 'C' in blue, 'D' in grey, etc.</p>
  <pre><code>df=pd.DataFrame({'a':['A','B','D'],'b':['E','B','C'],'c':['F','A','D']})
  </code></pre>
  <p>How can I achieve this using the <code>Styler.apply</code>? Any thoughts?</p>