I can create beatiful scatter plot with seaborns regplot, obtain the right level of transparency through the scatter_kws as in
sns.regplot(x='logAssets', y='logLTIFR', lowess=True, data=df, scatter_kws={'alpha':0.15}, line_kws={'color': 'red'})
and obtain this:
Is there an option in a seaborn pairplot to tweak transparency?

