def znes_colors(n=None):
    """Return dict with ZNES colors.

    Examples
    --------
    >>> znes_colors().keys()  # doctest: +ELLIPSIS
    dict_keys(['darkblue', 'red', 'lightblue', 'orange', 'grey',...

    Original author: @ckaldemeyer
    """
    colors = {
        'darkblue': '#00395B',
        'red': '#B54036',
        'lightblue': '#74ADC0',
        'orange': '#EC6707',
        'grey': '#BFBFBF',
        'dimgrey': 'dimgrey',
        'lightgrey': 'lightgrey',
        'slategrey': 'slategrey',
        'darkgrey': '#A9A9A9'
    }

    # allow for a dict of n colors
    if n is not None:
        if n > len(colors):
            raise IndexError('Number of requested colors is too big.')
        else:
            return {k: colors[k] for k in list(colors)[:n]}
    else:
        return colors