A bit has been personal experience, just the general change in the feel of a room when a minority walks into it. I'm a minority myself and am attuned to the little social cues that pop up, and I catch it when I'm in Williamsburg or Park Slope on weekends. It's when you know you're going to be that "I have an Indian friend/Arabic friend" in someone's future stories when you've only met the person for an evening or two. For a less personal anecdote, I would point to the controversies surrounding the Prime 6 hip hop club in Park Slope and the rap ban in Savalas. Basically it's non-native New Yorkers, the majority white, who have moved to western Brooklyn in recent years and gentrified it to the point where they're essentially pushing anyone not like them.