I'm not too sure about the colours, however, I do know how to switch themes.
First, make sure you have the Gnome themes installed. I'm assuming you are asking about FC2, so use the command:
rpm -qa | grep gnome-themes
Then, go to your main menu, then go to Preferences and Theme. You can mess around with each individual theme to customize it, but I've never done it so I can't give you anymore details.
Hope this helps.