title: pandas plot dataframe barplot with colors by category
body: <p>I would like to use pandas to plot a barplot with diffrent colors for category in column.</p>
  
  <p>Here is a simple example: (index is variable)</p>
  
  <pre><code>df:
           value   group
  variable               
  a             10      1
  b              9      1
  c              8      1
  d              7      2
  f              6      2
  g              5      3
  h              4      3
  </code></pre>
  
  <p>I would like to make a barplot with coloring on group. I would also like to specify the colors. In my original dataset I have many goups.
  Could someone help me with this?</p>