How to set the default color cycle for all subplots with matplotlib?

Starting from matplotlib 1.5, mpl.rcParams['axes.color_cycle'] is deprecated. You should use axes.prop_cycle:

import matplotlib as mpl
mpl.rcParams['axes.prop_cycle'] = mpl.cycler(color=["r", "#e94cdc", "0.7"]) 

Sure! Either specify axes.color_cycle in your .matplotlibrc file or set it at runtime using matplotlib.rcParams or matplotlib.rc.

As an example of the latter:

import matplotlib.pyplot as plt
import matplotlib as mpl
import numpy as np

# Set the default color cycle
mpl.rcParams['axes.prop_cycle'] = mpl.cycler(color=["r", "k", "c"]) 

x = np.linspace(0, 20, 100)

fig, axes = plt.subplots(nrows=2)

for i in range(10):
    axes[0].plot(x, i * (x - 10)**2)

for i in range(10):
    axes[1].plot(x, i * np.cos(x))

plt.show()

In the version of 2.1.0, the below works for me, using set_prop_cycle and module cycler

from cycler import cycler
custom_cycler = (cycler(color=['r','b','m','g']))
ax.set_prop_cycle(custom_cycler)

you can add additional line attribute

custom_cycler = (cycler(color=['r','b','m','g']) + cycler(lw=[1,1,1,2]))

'ax' comes from ax=plt.axes() or any axes generator