How to create a matplotlib colormap that treats one value specially?

To create a matplotlib colormap that treats one value specially, we can take the following steps −

Set the figure size and adjust the padding between and around the subplots.
Get a colormap instance, name is "rainbow".
Set the color for low out-of-range values, using set_under('red') method.
Create random data and eps using numpy.
Create a figure and a set of subplots.
Display data as an image, i.e., on a 2D regular raster, using imshow() method.
Create a colorbar for a ScalarMappable instance, im.
To display the figure, use show() method.

Example

import matplotlib.pyplot as plt
import numpy as np

plt.rcParams["figure.figsize"] = [7.50, 3.50]
plt.rcParams["figure.autolayout"] = True

cmap = plt.get_cmap('rainbow')
cmap.set_under('red')

data = np.random.randn(5, 5)
eps = np.spacing(0.0)

fig, ax = plt.subplots()
im = ax.imshow(data, interpolation='nearest', vmin=eps, cmap=cmap)
fig.colorbar(im, extend='min')

plt.show()