Answer: matplotlib: binary heat plot

You need what's known as a ListedColorMap:

import numpy as np
import matplotlib.pyplot as plt
import matplotlib as mpl

# random data
x = np.random.random_integers(0, 1, (10, 10))

fig, ax = plt.subplots()

# define the colors
cmap = mpl.colors.ListedColormap(['r', 'k'])

# create a normalize object the describes the limits