Hi Dan Kinchen,
Please accept our apology for the misunderstanding.
You are right that there isn't a single property like HeaderBackground that can be used to implement the described scenario. Therefore I wanted to ask you to elaborate on what do you expect such a property to do and also if you expect the RadTabControl and/or the RadTabItems to have such a property.
However, for now, except Style, you can implement this scenario using a HeaderTemplate and defining a border around each tab header. If you define two HeaderTemplates for the RadTabItems and set a border in them with a proper background, you can set a different HeaderTemplate for each TabItem depending on your custom logic.
I prepared a sample project illustrating this approach. Give it a try and let us know if it works for you.
the Telerik team
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