From the Yum Extender FAQ [link]
Q. What does the package colors mean ?
Red = Package is a update to a installed package.Blue = Package is obsoleting a installed package.Green = Package is installed.Black = Available package.
Q. What does the "green plus " / "star on rectangle (document)" means ?
The "green plus " / "star on rectangle" means that a packages is recent.
- If it is in the update/install view it means that this version of the package has been added to the repository in the last 14 days.
- If it is in the remove view it means that the package as been installed on the system in the last 14 days.