cdict1 = {'red': ((0.0, 0.0, 0.0), (0.5, 0.0, 0.1), (1.0, 1.0, 1.0)),
    'green': ((0.0, 0.0, 0.0), (1.0, 0.0, 0.0)), 'blue': ((0.0, 0.0, 1.0),
    (0.5, 0.1, 0.0), (1.0, 0.0, 0.0))}
blue_red1 = mpl.colors.LinearSegmentedColormap('BlueRed1', cdict1)
blue_red1_r = reverse_colourmap(blue_red1)
fig = plt.figure(figsize=(8, 2))
ax1 = fig.add_axes([0.05, 0.8, 0.9, 0.15])
ax2 = fig.add_axes([0.05, 0.475, 0.9, 0.15])
norm = mpl.colors.Normalize(vmin=0, vmax=1)
cb1 = mpl.colorbar.ColorbarBase(ax1, cmap=blue_red1, norm=norm, orientation
    ='horizontal')
cb2 = mpl.colorbar.ColorbarBase(ax2, cmap=blue_red1_r, norm=norm,
    orientation='horizontal')
Invert colormap in matplotlib