Seaborn-compatible hexbin plot.

    See also: http://seaborn.pydata.org/tutorial/axis_grids.html#mapping-custom-functions-onto-the-grid

def hexbin(x, y, color="purple", **kwargs):
    """Seaborn-compatible hexbin plot.

    See also: http://seaborn.pydata.org/tutorial/axis_grids.html#mapping-custom-functions-onto-the-grid
    """
    if HAS_SEABORN:
        cmap = sns.light_palette(color, as_cmap=True)
    else:
        cmap = "Purples"
    plt.hexbin(x, y, cmap=cmap, **kwargs)