title: Adjust colorbar matplotlib using TwoSlopeNorm
body: <p>I know there are similar questions out there, but I haven't managed to solve my problem. I followed the advice in this post (<a href="https://stackoverflow.com/questions/20144529/shifted-colorbar-matplotlib/73526149#73526149">Shifted colorbar matplotlib</a>) and used TwoSlopeNorm to shift my colorbar to have negative values with blue colours and positive values with red colours (example code below). But for some reason two intervals (0-5 and 5-10) are assigned white. Then two intervals have the same red (15-20 and 20-25). How do I fix this to have different colours for each interval?</p>
  <pre><code>fig, axes = plt.subplots()
  levels = np.linspace(-5, 25, 7)
      
  im0 = da6_annualtmn.plot.contourf(norm=TwoSlopeNorm(vcenter=0), 
                                    cmap='bwr', extend='max', levels=levels)
  </code></pre>
  <p><a href="https://i.stack.imgur.com/945EK.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/945EK.png" alt="enter image description here" /></a></p>