color2 = colorConverter.to_rgba('black')
cmap1 = mpl.colors.LinearSegmentedColormap.from_list('my_cmap', ['green',
    'blue'], 256)
cmap2 = mpl.colors.LinearSegmentedColormap.from_list('my_cmap2', [color1,
    color2], 256)
cmap2._init()
alphas = np.linspace(0, 0.8, cmap2.N + 3)
cmap2._lut[:, (-1)] = alphas
img2 = plt.imshow(zvals, interpolation='nearest', cmap=cmap1, origin='lower')
img3 = plt.imshow(zvals2, interpolation='nearest', cmap=cmap2, origin='lower')
plt.show()
Наложение графиков imshow в matplotlib