GTK+ 1.2/2.0
The theme engine is based on the Redhat 8.0 Bluecurve theme. It features a nondistracting clean look with neutral yet warmish colours taking into account UI usability issues.
For more information about the UI usability issues read the article "Thoughts & UI Clean-Ups on a Random Red Hat/Gnome2 Screenshot" on OSNews.com.
If you want the same little offset at the start and end of the row of tabs as can be seen in the first screenshot, you need to patch GTK+. The patch is included in the tarball of the theme engine.
You can also download the patch and already patched GTK+ rpms for Redhat 8.0 from here.