#!/usr/bin/env python3
# -*- coding: utf-8 -*-
import numpy as np
import matplotlib.pyplot as plt

img = np.random.rand(5, 10)
alpha = 0.5

plt.subplot(1, 2, 1)
plt.imshow(img, alpha=alpha, cmap='RdBu')
plt.colorbar(extend='both', orientation='horizontal', label='Current behaviour')

# Temporary fix to manually set the alpha of the extend patches
# doesn't look perfect, but is an improvement over the current behaviour
plt.subplot(1, 2, 2)
plt.imshow(img, alpha=alpha, cmap='RdBu')
cb = plt.colorbar(extend='both', orientation='horizontal', label='Temporary fix')
for patch in cb._extend_patches:
    patch.set_alpha(alpha)

plt.show()