Server Statistics - What do the Two Different Colors Represent?

I have the monitoring plug-in installed. What do the two different colors in the server statistics represent? Is there any document that describes the various statistics?

Can someone provide some insight into what the colors (blue and orange) on the Server Traffic reports mean? See the attached file for an example.

We are looking to roll Openfire out to several offices and need some guestimate regarding the network utilization.