I did a quick Google search, and while I didn't see anyone reporting on the most recent study, apparently the study from the previous season revealed "79.8% of attendees during the 2014-2015 season were Caucasian, which follows a similar pattern in ethnic attendance since 1998."
As I'm sure you know, there's a big chicken-or-the-egg discussion about whether producers don't produce more kinds of stories with more kinds of casts because the audience isn't there, or whether the audience isn't there because they aren't seeing themselves reflected on stage (and producers often don't know how to reach them).
