RadAutoCompleteBox：删除第一行的突出显示

Question

默认情况下，telerik中的第一行：RadAutoCompleteBox始终以深灰色突出显示，我该如何删除此突出显示？

我的xalm代码：

<StackPanel Grid.Row="1" Grid.Column="1" VerticalAlignment="Center">
<telerik:RadAutoCompleteBox     WatermarkContent="Enter data"
                                VerticalAlignment="Center"
                                x:Name="companiesAutoCompleteBox"
                                TextSearchMode="StartsWith"
                                AutoCompleteMode="Suggest"
                                SelectionMode="Single"
                                TextSearchPath="Name"
                                ItemsSource="{Binding DataList}"
                                DropDownItemTemplate="{DynamicResource CompaniesSearchAutoComplete}"
                                SelectionChanged="dataAutoCompleteBoxSelectionChanged"
                                SearchTextChanged="dataSearchTextChanged" />