def _colormap_plot_ppsd(cmaps):
    """
    Plot for illustrating colormaps: PPSD.

    :param cmaps: list of :class:`~matplotlib.colors.Colormap`
    :rtype: None
    """
    import matplotlib.pyplot as plt
    from obspy import read
    from obspy.signal import PPSD
    from obspy.io.xseed import Parser
    st = read('https://examples.obspy.org/BW.KW1..EHZ.D.2011.037')
    st += read('https://examples.obspy.org/BW.KW1..EHZ.D.2011.038')
    parser = Parser('https://examples.obspy.org/dataless.seed.BW_KW1')
    ppsd = PPSD(st[0].stats, metadata=parser)
    ppsd.add(st)
    for cmap in cmaps:
        ppsd.plot(cmap=cmap, show=False)
    plt.show()
