Bug report

Bug summary

When saving a 3D scatter plot with a color bar using savefig (either plt.savefig or fig.savefig), the data point colors are incorrect on the saved image, however the inline image (I'm using jupyter lab notebooks) is fine, the issue is only present when saving the figure. Note that this only happens when a colorbar is added to the figure, when a figure with points colored according to a set of values is saved, the issue does not occur. So it would seem that this issue is caused by some interaction of savefig and colorbar.

I've tried both matplotlib version 3.3.1 and 3.3.2 and in both versions this occurs. I've also tried downgrading to version 3.2.1, in version 3.2.1 this does not occur, so it seems some change in 3.3.1 is the cause of this issue.

Code for reproduction

Requirements: matplotlib 3.3.1 or 3.3.2

The following requirements are purely for setting up an example dataset which I used in the following code snippet to generate an example dataset to plot, as such I'm not listing the version numbers.

Optional: pandas, numpy

Also note that I used JupyterLab notebook to run the code, although given that I was able to 'fix' the issue by downgrading to matplotlib version 3.2.1 I don't think there is any link between running the code in JupyterLab and the issue itself.

#importing packages 
import matplotlib.pyplot as plt

import numpy as np
import itertools
import pandas as pd

# example data setup 
data = list(itertools.product(*[np.arange(0, 5, 1), np.arange(0, 5, 1), np.arange(0, 5, 1)]))
df = pd.DataFrame(data, columns=['x', 'y', 'z'])

df['c'] = df['x'] + df['y']

# plotting

## no color bar example (no issue)

fig = plt.figure()
ax = fig.add_subplot(111, projection='3d', proj_type = 'ortho')

sc = ax.scatter(
    df['x'], 
    df['y'],
    df['z'],
    c=df['c'],
    s=40  # size is purely to make it easier to see
)  

plt.savefig('example no colorbar save.png')  # dpi has no effect, purely to make it easier to zoom into the figure

## color bar example (ISSUE)

fig = plt.figure()
ax = fig.add_subplot(111, projection='3d', proj_type = 'ortho')

sc = ax.scatter(
    df['x'], 
    df['y'],
    df['z'],
    c=df['c'],
    s=40  # size is purely to make it easier to see
)  

fig.colorbar(sc)

plt.savefig('example colorbar save.png', dpi=300)  # dpi has no effect, purely to make it easier to zoom into the figure

Actual outcome

This is being the saved figure with a color bar (note that if you zoom in the outlines of the data points are correct - see expected outcome below - but the fill of the points is incorrect).

Note that if no colorbar is added, the plot saves correctly as shown below.

Expected outcome

This is a screenshot of the colorbar chart as it is shown inline in the JupyterLab notebook.

And this is a screenshot of the non colorbar chart as it is shown inline in the JupyterLab notebook, note this one is essentially the exact same as the saved version, so the issue is purely with the colorbar/savefig interaction.

Matplotlib version

• Operating system: Windows 10
• Matplotlib version: 3.3.2
• Matplotlib backend (print(matplotlib.get_backend())):
• Python version: 3.8.5
• Jupyter version (if applicable): 2.2.6
• Other libraries: pandas, numpy, itertools (python built in library)

Everything has been installed via conda, with all packages listed being install from the default channel.