Setting is important - there needs to be honesty, accessibility, not too staged. Grad student reluctance and apathy - hard to make community a priority for busy grad students. Underrepresented students have their own sub-communities. Sometimes it takes an event to bring students together. Easier to have casual contacts among undergrads but that process isn't initiated for grads.
Joint sponsorship is a way to solve that.
Joint events that are non-cultural in nature can work. We can do that by having international food booths at big events. Drawing from undergrad population can help, too. Should just try to find racial issues that everyone cares about. Think carefully about how an issue is framed.