Bug report

Bug summary

hlines and vlines color does not default to lines.color in rcParams. The default argument is 'k' which doesn't work with dark backgrounds.

Code for reproduction

import matplotlib.pyplot as plt
import matplotlib as mpl
plt.style.use('dark_background')

plt.figure()
with mpl.rc_context({'lines.color':'white'}):
   plt.hlines(0.5, 0, 1) # defaults to a black line, which doesn't work with a dark background
   plt.vlines(0.5, 0, 1, colors=None) # This will fall back to `lines.color`

Actual outcome

Expected outcome

Matplotlib version

• Operating system: Windows 10
• Matplotlib version: 3.1.2
• Matplotlib backend (print(matplotlib.get_backend())): module://ipykernel.pylab.backend_inline
• Python version: 3.7.4
• Jupyter version (if applicable):
• Other libraries: