Matplotlib でカラーバー範囲を設定して特定のデータ値を強調表示するにはどうすればよいですか?

<code class="python">import matplotlib.pyplot as plt
import numpy as np

# Create a custom colormap
cdict = {
  'red'  :  ( (0.0, 0.25, .25), (0.02, .59, .59), (1., 1., 1.)),
  'green':  ( (0.0, 0.0, 0.0), (0.02, .45, .45), (1., .97, .97)),
  'blue' :  ( (0.0, 1.0, 1.0), (0.02, .75, .75), (1., 0.45, 0.45))
}
cm = plt.colors.LinearSegmentedColormap('my_colormap', cdict, 1024)

# Create some data
x = np.arange(0, 10, .1)
y = np.arange(0, 10, .1)
X, Y = np.meshgrid(x,y)
data = 2*( np.sin(X) + np.sin(3*Y) )

# Plot the data with a custom colorbar range
plt.pcolor(X, Y, data, cmap=cm, vmin=-4, vmax=4)
plt.colorbar()
plt.show()</code>