title: Setting background color to white when using cmap with a gradient that doesn't contains white
body: <p>So I have this matrix, which is defined as follows:</p>
  
  <pre><code>for row in range (0,squareSize):
              for col in range (0,squareSize):
                  if new_matrix[row][col]==1:
                      new_matrix[row][col]=color_matrix[row][col] #gradient given by values in color_matrix 
                  if new_matrix[row][col]==2:
                      new_matrix[row][col]=150 #color red
                  if new_matrix[row][col]==0:
                      new_matrix[row][col]=100 #color purple
  </code></pre>
  
  <p>SquareSize is 185, the entries which are zero are the points inside the circle, and the entries which are 2 are the ones inside the square but outside the circle.
  Both of them are mapped to different colors, and the rest is mapped according to a color gradient given by: </p>
  
  <pre><code>cmap = mpl.cm.hsv
  </code></pre>
  
  <p>After plotting it using:</p>
  
  <pre><code>plt.matshow(new_matrix, interpolation='nearest',cmap=cmap)
  </code></pre>
  
  <p>This is the output: <a href="https://i.stack.imgur.com/citQU.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/citQU.png" alt="enter image description here"></a></p>
  
  <p>However, I want the circle to be white... which is not part of the gradient colors :( How can I do that?</p>