How to plot the body of violin-plot on top of span rectangle?

Question

I want to do a violin-plot on top of a background color. I use axvspan to create the background. My problem is: I can't find a way to make the body of the violin-plot (the violin shape) appears on top of background color. It is only visible through the transparency of the background. Since violin-plot doesn't recognize the zorder command, is there a way to have the violin-plot on top of everything?

For example:

import numpy as np
import matplotlib.pyplot as plt

plt.figure()
plt.axvspan(-5,0,color='r' ,alpha =0.5)
plt.axvspan(0,5,color='g' ,alpha =0.5)
plt.violinplot(np.random.normal(0,1,100), vert = False)

One can see that the blue color of the violin shape appears in the transparency of the background colors (red and green). I want the blue color of the density shape to be on top of everything.

Answer 1

This question is similar to the Changing the color of matplotlib's violin plots though not exactly the same. I won't repeat what Nick T has written in his answer (make sure to thank him as well), but just add that PolyCollection has also set_alpha and set_zorder methods, which you could use like this:

plt.figure()
plt.axvspan(-5, 0, color='r', alpha=0.5, zorder=1)
plt.axvspan(0, 5, color='g', alpha=0.5, zorder=1)
parts = plt.violinplot(np.random.normal(0, 1, 100), vert=False)
parts['bodies'][0].set_alpha(0.8)
parts['bodies'][0].set_zorder(2)

Gives: