[Python] Matplotlib stacked histogram problem with alpha

I want to plot two data sets in a histogram using stacked = True but setting the alpha parameter is not working correctly. The colors of the histograms just get lighter instead of transparent. Have a look for yourself:

import matplotlib.pyplot as plt
import numpy as np

np.random.seed(123)

mu_x = 200
sigma_x = 25
x = np.random.normal(mu_x, sigma_x, size=100)

mu_x = 150
sigma_x = 25
y = np.random.normal(mu_x, sigma_x, size=100)

plt.hist([x,y], stacked=True, alpha=0.5, bins=10)

plt.show()


I tried defining colors for the histograms like plt.hist([x,y], color = [(0, 0, 1, 0.3),(1, 0, 0, 0.3) stacked=True, bins=10) but the problem stays the same.

Does anybody know how to solve this?



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