title: Matplotlib python change single color in colormap
body: <p>I use the colormap in python to plot and analyse values in a matrix. I need to associate the white color to each element equal to 0.0 while for others I'd like to have a "traditional" color map. Looking at  <a href="https://stackoverflow.com/questions/9893440/python-matplotlib-colormap">Python Matplotlib Colormap</a> I modified the dictionary used by pcolor as:</p>
  
  <pre><code>dic = {'red': ((0., 1, 1), 
                 (0.00000000001, 0, 0), 
                 (0.66, 1, 1), 
                 (0.89,1, 1), 
                 (1, 0.5, 0.5)), 
         'green': ((0., 1, 1), 
                  (0.00000000001, 0, 0), 
                  (0.375,1, 1), 
                  (0.64,1, 1), 
                  (0.91,0,0), 
                  (1, 0, 0)), 
         'blue': ((0., 1, 1), 
                 (0.00000000001, 1, 1), 
                 (0.34, 1, 1), 
                 (0.65,0, 0), 
                 (1, 0, 0))}
  </code></pre>
  
  <p>The result is:<img src="https://i.stack.imgur.com/zKEFm.png" alt="enter image description here"></p>
  
  <p>I set:</p>
  
  <pre><code>matrix[0][0]=0 matrix[0][1]=0.002
  </code></pre>
  
  <p>But as you can see they are both associated with the white color, even if I set 0.00000000001 as the starting point for the blue. How is this possible? How can I change it in order to obtain what I'd like?</p>