g = sns.pairplot(iris, hue='species', palette='husl', markers='d', size=2.5, plot_kws=
    {
    "s":40,
    "alpha":1.0,
    'lw':0.5,
    'edgecolor':'k'
    })

handles = g._legend_data.values()
labels = g._legend_data.keys()
g.fig.legend(handles=handles, labels=labels, loc='upper center', ncol=1)
g.fig.legend(handles=handles, labels=labels, loc='lower center', ncol=3)
g.fig.legend(handles=handles, labels=labels, loc='upper left', ncol=3)
g.fig.subplots_adjust(top=0.92, bottom=0.08)