import numpy as np
import matplotlib.pyplot as plt

fig = plt.figure()
plt.imshow(5*np.random.randn(100,100)+5, norm=plt.Normalize(-10, 10))
cb = plt.colorbar()
cb.set_limits(0, 10)

fig = plt.figure()
plt.imshow(5*np.random.randn(100,100)+5, norm=plt.Normalize(-10, 10))
cb = plt.colorbar(extend='both')

plt.show()