title: Sklearn Confusion Matrix: How to get the blue color
body: <p>when I plot my confusion matrix using this code</p>
  <pre><code>from sklearn.metrics import confusion_matrix, ConfusionMatrixDisplay
  cm = confusion_matrix(y_test, rmc_pred, labels=rmc.classes_)
  
  disp = ConfusionMatrixDisplay(confusion_matrix=cm,
                                  display_labels=rmc.classes_)
  
  
  disp.plot() 
  </code></pre>
  <p>I get a matrix in the colours purple, yellow, blue and green and there are vertical and horizontal lines cutting each row. I want to get a blue coloured confusion matrix looking like in the documentation of sklearn. Could anybody of you help me with how to do so?
  Many thanks in advance!</p>
  <p>If I use sklearns function plot_confusion_matrix with the cmap parameter I receive an error message stating: The number of FixedLocator locations (9), usually from a call to set_ticks, does not match the number of ticklabels (10).</p>