title: Changing color of bar plot if value is less than zero and fill white space
body: <p>I have created a DataFrame:</p>
  
  <pre><code>df.tail(20)
         Speed
  130 -0.000272
  131 -0.000219
  132 -0.000178
  133 -0.000234
  134 -0.000261
  135 -0.000281
  136 -0.000244
  137 -0.000255
  138 -0.000290
  139 -0.000210
  140 -0.000216
  141 -0.000209
  142 -0.000139
  143 -0.000060
  144  0.000007
  145  0.000043
  146  0.000068
  147  0.000093
  148 -0.000025
  149 -0.000005
  </code></pre>
  
  <p>I am using a barchart to draw barplot:</p>
  
  <pre><code>ind = np.arange(len(df))
  ax.bar(ind, df['Speed'], width=0.5, color="r")
  </code></pre>
  
  <p>What I am trying to do is changing bar colors to red if values are less than zero and green if they are higher than zero. And show smooth graph instead of bars with white spaces.</p>
  
  <p>Thanks</p>