Override DataGridColumnHeaderBackgroundColor to Transparent to match refreshed UX.

code/TemplateStudioForWinUICs/Templates/Pg/DGrid/Param_ProjectName/Views/Param_ItemNamePage.xaml

@@ -12,6 +12,9 @@
             AutoGenerateColumns="False"
             GridLinesVisibility="Horizontal"
             ItemsSource="{x:Bind ViewModel.Source, Mode=OneWay}">
+            <controls:DataGrid.Resources>
+                <SolidColorBrush x:Key="DataGridColumnHeaderBackgroundColor" Color="Transparent"/>
+            </controls:DataGrid.Resources>
             <controls:DataGrid.Columns>
                 <!-- TODO: Replace column definitions to match real data. Consider adding Header values to Resources.resw. -->
                 <controls:DataGridTextColumn Binding="{Binding OrderID}" Header="OrderID" />