Action Hook for Changing Roles via User Grid

Greetings,

I’d like to trigger an event when roles are modified via the user grid (“Add role” and “Remove role” dropdowns) and was wondering if there is an appropriate hook for this? I browsed the code but couldn’t figure out what to use.

Basically, whenever a user or users role(s) is/are changed (individually, or in bulk via the checkboxes are changed, also from the user editor page), I’d like to trigger an action where I modify a value in wp_usermeta.

Thank you,
Daniel