Hello Tim Lushbough,
There is a fairly simple way of customizing the filtering control of RadGridView. Attached I am sending you a sample to get you started on the task. In it you will find a RadGridView with a column defined in XAML. In the FilteringControl property of that column I have placed the default filtering control and edited its template so I you can make all the adjustments.
Let me know if you need any further assistance with this.
the Telerik team
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