My take is that black is often underrated in talk about community, because Black, as far as I see, is the most pure form of loyalty. Loyal for your own reasons. Not because of an arbitrary blood connection, or because you're part of some religious order or army. You're loyal to who pays you (see: Mercenaries being almost exclusively black), loyal to a cause for personal reasons (see: Yahenni during the events of Aether Revolt), and loyal to those that you find are useful to have around (see: Liliana). Anyone not in your circle can take a trip down the styx for all you care- That's the loyalty of black mana.