"And give me some coffee. Black as midnight on a moonless night." Harga looked surprised. That wasn't like Vimes. "How black's that, then?" he said. "Oh, pretty damn black, I should think." "Not necessarily." "What?" "You get more stars on a moonless night. Stands to reason. They show up more. It can be quite bright on a moonless night." Vimes sighed. "An overcast moonless night?" he said. Harga looked carefully at his coffee pot. "Cumulus or cirro-nimbus?" "I'm sorry? What did you say?" "You get city lights reflected off cumulus, because it's low lying, see. Mind you, you can get high-altitude scatter off the ice crystals in--" "A moonless night," said Vimes, in a hollow voice, "that is as black as coffee."