You can change the background colour of your network chart with fig.set_facecolor(). Note that you need to add fig.get_facecolor if you want to keep your background colour for your png.
# libraries
import pandas as pd
import numpy as np
import networkx as nx
import matplotlib.pyplot as plt
# Build a dataframe with your connections
df = pd.DataFrame({ 'from':['A', 'B', 'C','A'], 'to':['D', 'A', 'E','C'] })
df
# Build your graph
G=nx.from_pandas_dataframe(df, 'from', 'to', create_using=nx.Graph() )
# Custom the nodes:
fig = plt.figure()
nx.draw(G, with_labels=True, node_color='skyblue', node_size=1500, edge_color='white')
fig.set_facecolor("#00000F")
# If you want to save the figure to png:
# plt.savefig('yourname.png', facecolor=fig.get_facecolor() )
