I think it was a bit of sarcasm/reality in the statement. Saying something is "the new black" is the way of saying its the new fad. So if he said volunteerism is the new black, he's saying it's in right now. But who knows if it will stay on people's minds to remember the cause. If people had kept the cause in their hearts/minds/efforts 20 years ago, Live 8 wouldn't have been necessary.