coming from someone who has a lot of guy friends, in this case referring to the black ones, these nicknames most likely means the guy is comfortable around you, he digs your friendship, and could possibly see you as girlfriend material. try to pay close attention to the context of how he uses them. on the other hand, some guys just use them 24/7.
It's a good thing. Stupid. But it's a good thing. It's like letting you know you're okay in their book, and sometimes guys call their girlfriends "shawty"