Python Matplotlib Boxplot Color

To colorize the boxplot, you need to first use the patch_artist=True keyword to tell it that the boxes are patches and not just paths. Then you have two main options here:

1. set the color via ...props keyword argument, e.g.
   boxprops=dict(facecolor="red"). For all keyword arguments, refer to the documentation
2. Use the plt.setp(item, properties) functionality to set the properties of the boxes, whiskers, fliers, medians, caps.
3. obtain the individual items of the boxes from the returned dictionary and use item.set_<property>(...) on them individually. This option is detailed in an answer to the following question: python matplotlib filled boxplots, where it allows to change the color of the individual boxes separately.

The complete example, showing options 1 and 2:

import matplotlib.pyplot as plt
import numpy as np
data = np.random.normal(0.1, size=(100,6))
data[76:79,:] = np.ones((3,6))+0.2

plt.figure(figsize=(4,3))
# option 1, specify props dictionaries
c = "red"
plt.boxplot(data[:,:3], positions=[1,2,3], notch=True, patch_artist=True,
            boxprops=dict(facecolor=c, color=c),
            capprops=dict(color=c),
            whiskerprops=dict(color=c),
            flierprops=dict(color=c, markeredgecolor=c),
            medianprops=dict(color=c),
            )


# option 2, set all colors individually
c2 = "purple"
box1 = plt.boxplot(data[:,::-2]+1, positions=[1.5,2.5,3.5], notch=True, patch_artist=True)
for item in ['boxes', 'whiskers', 'fliers', 'medians', 'caps']:
        plt.setp(box1[item], color=c2)
plt.setp(box1["boxes"], facecolor=c2)
plt.setp(box1["fliers"], markeredgecolor=c2)
            

plt.xlim(0.5,4)
plt.xticks([1,2,3], [1,2,3])
plt.show()