Make seaborn show a colorbar instead of a legend when using hue in a bar plot?

The other answer is a bit hacky. So a more stringent solution, without producing plots that are deleted afterwards, would involve the manual creation of a ScalarMappable as input for the colorbar.

import matplotlib.pyplot as plt
import seaborn as sns
titanic = sns.load_dataset("titanic")
g = titanic.groupby('pclass')
survival_rates = g['survived'].mean()
n = g.size()

norm = plt.Normalize(survival_rates.min(), survival_rates.max())
sm = plt.cm.ScalarMappable(cmap="Reds", norm=norm)
sm.set_array([])

ax = sns.barplot(x=n.index, y=n, hue=survival_rates, palette='Reds', 
                 dodge=False)

ax.set_ylabel('n passengers')
ax.get_legend().remove()
ax.figure.colorbar(sm)

plt.show()

You can try this:

import matplotlib.pyplot as plt
import seaborn as sns
titanic = sns.load_dataset("titanic")
g = titanic.groupby('pclass')
survival_rates = g['survived'].mean()
n = g.size()

plot = plt.scatter(n.index, n, c=survival_rates, cmap='Reds')
plt.clf()
plt.colorbar(plot)
ax = sns.barplot(x=n.index, y=n, hue=survival_rates, palette='Reds', dodge=False)
ax.set_ylabel('n passengers')
ax.legend_.remove()

Output: