Topic, Red and black numbers next to topics?

  Okay, thanks.

  This topic's less than one day old, so it has no black numbers.

  Red numbers= The posts of the day before
Black numbers= All posts

And when the just red numbers on a topic the topic has just posts from the day before (or the topic was created the day before)

  http://www.bonuslevel.org/forum/topic_3859.html

  I've been gone for about a week because of my very dodgy Internet connection, and I want to know about the red and black numbers next to the forums in the forum list, and why there aren't any black numbers next to some forums?