title: Split pandas dataframe conditionally to plot with different colors
body: <p>I have pandas dataframe with pair of values and like to color code it conditionally such as</p>
  
  <p><code>df.plot(kind='scatter', ax=ax1, x='a', y='b', c=np.where(['a']&gt;0.5, 'r', 'g']))</code></p>
  
  <p>But not getting anywhere. Applying same condition on both <code>a</code> and <code>b</code> is ultimate objective. Any lead is appreciative.</p>