title: Using multiple colors in matplotlib plot
body: <p>I have a numpy array of 2D data points (x,y), which are classified into three categories (0,1,2).</p>
  
  <pre><code>a = array([[ 1, 2, 3, 4, 5, 6, 7, 8 ],
             [ 9, 8, 7, 6, 5, 4, 3, 2 ]])
  
  class = array([0, 2, 1, 1, 1, 2, 0, 0])
  </code></pre>
  
  <p>My question is if I can plot these points with multiple colors. I would like to do something like this:</p>
  
  <pre><code>colors = list()
  for i in class:
      if i == 0:
          colors.append('r')
      elif i == 1:
          colors.append('g')
      else:
          colors.append('b')
  
  print colors
  ['r', 'b', 'g', 'g', 'g', 'b', 'r', 'r']
  
  pp.plot(a[0], a[1], color = colors)
  </code></pre>