I attached a sample project demonstarting your requirement. Some notes about it -- please add reference to NoXAML assemblies to be able to run it (from Binaries.NoXAML folder under your controls local installation path) as the test project is made with the use of our implicit styles theming mechanism. When it comes to custom styles where you don't practically change the control template (as in this case) and you want to support theme change runtime, we highly recommend the implicit styles theming mechanism. You mind find more details about it in our documentation here
About the project -- I added a custom attached boolean property to the RadTabItem and it triggers an animation that changes the background color of the TabItem. The boolean property won't turn on for the first tab item if it is selected. If you just switch to the next tab, the first one won't get highlighted as well. However on timer tick which is set to 3 sec when we update a sample collection of list items the attached boolean property turns on and the "highlight" tab animation kicks in.
Feel free to modify the attached project per your own needs.
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