The content of the RadBusyIndicator enters disabled state when the RadBusyIndicator is in busy mode. So the ListBox which is in the RadBusyIndicator is grayed out because it is in disabled state. This is the expected behavior.
If you wish to change this, the simplest thing to do is to move the ListBox out of the RadBusyIndicator content and simply arrange the visual elements so that the RadBusyIndicator appears on top of the ListBox. Another way of achieving the same effect is to customize the disabled state of the ListBoxItems to resemble their normal state. As you might notice, the latter is not a good method because it you will not know if a ListBoxItem is ever disabled.
I hope this helps.
the Telerik team
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