I was browsing this guilds website, and saw they were using this roster. They had alot of modifications though, one was the names of members appear in the color of thier class.

Here is thier site
http://wowredemption.com/roster

How can I do this on my site?

This is default behavior since roster version 1.7.0 (current version as of this post)

Although, I do say that this person has done a very nice job editing roster