title: Using a different cmap/color for one level in a contourf plot
body: <p>I am trying to do a matplotlib <code>contourf</code> plot with some <code>x</code>, <code>y</code>, and <code>z</code> values. Basically the <code>z</code> values will define the color of the plot.
  However, where I am at right now one region (i.e. the important region for me) is very small compared to the rest (see figure), so it can be very difficult to see this particular region actually (a few small black "dots"). So I was thinking if it was possible maybe to get the first lvl (or last level since it's negative values in this case) in another color, or maybe outline it with a thin white line or something, so one can really see the small and important dots ?</p>
  
  <p>I am plotting with this code:</p>
  
  <pre><code>import matplotlib.pyplot as plt
  from matplotlib import rcParams
  import matplotlib.colors as colors
  import numpy as np
  
  nx = 41
  ny = 67
  
  x = np.linspace(0.01, 1, nx)
  y = np.linspace(0.01, 2, ny)
  x_bc = x[:, np.newaxis]
  y_bc = y[np.newaxis, :]
  
  z = x_bc*y_bc
  
  max_value = np.amax(z)
  cmapp = plt.get_cmap('Greys')
  
  level_intervals = [100, 90, 80, 70, 60, 50, 40, 30, 20, 10, 8, 1.92, 0]
  level_list = [max_value-i for i in level_intervals]
  
  col_bar = plt.contourf(x, y, z.T, level_list, cmap=cmapp)
  plt.xlabel('x')
  plt.ylabel('y')
  plt.colorbar(col_bar, cmap=cmapp)
  
  plt.show()
  </code></pre>
  
  <p>I am sorry for not providing any real data, but I can't replicate the data used for the plot below (where there actually is some small amounts/dots of almost black, inside the almost black (weird sentence). However, the size and how the <code>z</code> data is created is just as above. There has, however, been many calculations in between before getting the data from the figure.</p>
  
  <p><a href="https://i.stack.imgur.com/OR5g2.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/OR5g2.png" alt="enter image description here"></a></p>