title: Multiple data in scatter matrix
body: <p>Is it possible to add multiple data to a <code>pandas.tools.plotting.scatter_matrix</code> and assigning a color to each group of data?</p>
  
  <p>I'd like to show the scatter plots with data points for one group of data, let's say, in green and the other group in red in the very same scatter matrix. The same should apply for the density plots on the diagonal.
  I know that this is possible by using matplotlib's <code>scatter</code> function, but that does not give me a scatter matrix.</p>
  
  <p>The documentation of pandas is mum on that.</p>