new_contents: """
  Line colors with a custom CPT
  -----------------------------
  
  The color of the lines made by :meth:`pygmt.Figure.plot` can be set according to a
  custom CPT and assigned with the ``pen`` argument.
  
  The custom CPT can be used by setting the plot command's ``cmap`` argument to ``True``. The
  ``zvalue`` argument sets the z-value (color) to be used from the custom CPT, and the line
  color is set as the z-value by using **+z** when setting the ``pen`` color.
  
  """
  
  import numpy as np
  import pygmt
  
  # Create a list of values between 20 and 30 with at 0.2 intervals
  x = np.arange(start=20, stop=30, step=0.2)
  
  fig = pygmt.Figure()
  fig.basemap(frame=["WSne", "af"], region=[20, 30, -10, 10])
  
  # Create a custom CPT with the batlow CPT and 10 discrete z-values (colors)
  pygmt.makecpt(cmap="batlow", series=[0, 10, 1])
  
  # Plot 10 lines and set a different z-value for each line
  for zvalue in range(0, 10):
      y = zvalue * np.sin(x)
      fig.plot(x=x, y=y, cmap=True, zvalue=zvalue, pen="thick,+z,-")
  # Color bar to show the custom CPT and the associated z-values
  fig.colorbar()
  fig.show()
  
subject: Add a gallery example of setting line colors with a custom CPT (#774)