bar takes a list of colors as an argument (docs). Simply pass in the colors you want.
import matplotlib.pyplot as plt
import matplotlib.cm as cm
from matplotlib.colors import Normalize
from numpy.random import rand
fig, ax = plt.subplots(1, 1)
# get a color map
my_cmap = cm.get_cmap('jet')
# get normalize function (takes data in range [vmin, vmax] -> [0, 1])
my_norm = Normalize(vmin=0, vmax=5)
# some boring fake data
my_data = 5*rand(5)
ax.bar(range(5), rand(5), color=my_cmap(my_norm(my_data)))
plt.show()
