I get the impression you live or spend most of your time in vibrant, perhaps wealthy neighborhoods like Williamsburg or just Manhattan. Your green cab story doesn't pan out in most of North Brooklyn outside of Williamsburg, they are invisible because the market dictates that it's too poor for them to bother to look for rides. Then there are the wealthier areas like Cobble Hill and Park Slope and so on - I wouldn't expect to see green cabs in Flatbush or something.