We already are setting the FilterEvaluationMode to UseCollectionView.  

Here's the code we use to override the background.  Again, everything works as expected with "Virtualize" but not with "Recycle".

<Style TargetType="{x:Type igData:SummaryResultPresenter}">
    <Setter Property="Template">
        <Setter.Value>
            <ControlTemplate TargetType="{x:Type igData:SummaryResultPresenter}">
                <Border
		            Background="{Binding Converter={StaticResource SummaryFieldBackgroundToColorConverter}}"
		            BorderBrush="{TemplateBinding BorderBrush}"
		            BorderThickness="0" Margin="0,0,0,0"
		            Padding="{TemplateBinding Padding}"
                    SnapsToDevicePixels="True"
                    ToolTip="{Binding Path=SummaryResult.ToolTipResolved, RelativeSource={RelativeSource TemplatedParent}}">
                    <TextBlock HorizontalAlignment="Right" Foreground="{Binding Converter={StaticResource SummaryFieldForegroundToColorConverter}}" Text="{Binding Path=SummaryResult.DisplayTextAsync, Mode=OneWay, RelativeSource={RelativeSource TemplatedParent}}"/>
                </Border>
            </ControlTemplate>
        </Setter.Value>
    </Setter>
</Style>

And here's our converter code

    public class SummaryBackgroundFieldToColorConverter : IValueConverter
    {
        public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
        {
            if (value == null) return null;
            var summaryResultEntry = value as SummaryResultEntry;

            var summaryValue = summaryResultEntry?.SummaryResult.Value;
            if (summaryValue == null) return null;

            double dblValue;
            if (!double.TryParse(summaryValue.ToString(), out dblValue) || dblValue == 0)
            {
                return null;
            }

            return dblValue < 0 ? Brushes.Red : Brushes.Green;
        }

        public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
        {
            return value;
        }
    }

In your example, make the following changes and then when you run it, group by "OrderID" and you should see how the averaged summation back colors aren't always correct.  Values over 50 should always be red but they aren't.   If you set the grid to "Virtualize", then the colors are always correct.  

Here's the SummaryResultPresenter Style

<Style TargetType="{x:Type igDP:SummaryResultPresenter}">
                <Setter Property="Padding" Value="1,1"/>
                <Setter Property="Template">
                    <Setter.Value>
                        <ControlTemplate TargetType="{x:Type igDP:SummaryResultPresenter}">
                            <Border
						Background="{Binding Converter={StaticResource bconverter}}"
						BorderBrush="{TemplateBinding BorderBrush}"
						BorderThickness="1"
						Padding="{TemplateBinding Padding}"
						ToolTip="{Binding Path=SummaryResult.ToolTipResolved, RelativeSource={RelativeSource TemplatedParent}}">
                                <!-- SSP 3/19/10 - Optimizations
                            Changed the binding to bind to the new DisplayTextAsync instead of the DisplayText so we
                            don't force synchronous calculation of the summary if it's dirty.
                        -->
                                <TextBlock  Text="{Binding Path=SummaryResult.DisplayTextAsync, Mode=OneWay,  RelativeSource={RelativeSource TemplatedParent}}"/>
                            </Border>
                        </ControlTemplate>
                    </Setter.Value>
                </Setter>
                <Setter Property="Margin" Value="0,0,0,2"/>
            </Style>

Here's the mainWindow Load Event (with some xamdatagrid settings)

 private void Window_Loaded(object sender, RoutedEventArgs e)
        {
            NwindDataSet nwind = new NwindDataSet();
            NwindDataSetTableAdapters.OrdersTableAdapter ord = new NwindDataSetTableAdapters.OrdersTableAdapter();
            ord.Fill(nwind.Orders);
            NwindDataSetTableAdapters.Order_DetailsTableAdapter ordd = new NwindDataSetTableAdapters.Order_DetailsTableAdapter();
            ordd.Fill(nwind.Order_Details);

            xamDataGrid1.DataSource = nwind.Orders.DefaultView;
            xamDataGrid1.FieldSettings.SummaryDisplayArea = SummaryDisplayAreas.InGroupByRecords;
            xamDataGrid1.FieldSettings.SummaryUIType = SummaryUIType.MultiSelect;
            xamDataGrid1.FieldLayoutSettings.GroupBySummaryDisplayMode = GroupBySummaryDisplayMode.SummaryCellsAlwaysBelowDescription;
            xamDataGrid1.FieldSettings.AllowEdit = false;

            loadSummary();
        }

Here's the Convert Method

public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
       {
           if (value == null) return null;
           var summaryResultEntry = value as SummaryResultEntry;

           var summaryValue = summaryResultEntry?.SummaryResult.Value;
           if (summaryValue == null) return null;

           double dblValue;
           if (!double.TryParse(summaryValue.ToString(), out dblValue))
           {
               return null;
           }

            return  dblValue > 50 ? "red" : "blue";
       }

Hello Andrew, 

I retested my sample with version 12.1 and everything is working as expected. However the loaded event code is causing the summary row to no longer appear because you have SummaryDisplayAreas set to InGroupByRecords, thus the element you would be interested in styling would be called GroupBySummariesPresenter. 

If  you change SummaryDisplayAreas to "TOP", and groupby OrderID and expand the child bands then the converter is working as expected along with the modified XAML. 

Are you trying to style the summaries when they're located inside the GroupbySummariesPresenter?

Yes, each Group Row should have a summary.  That's why SummaryDisplayArea is set to "InGroupByRecords".  When you run the sample with my changes, expand the main window out width wise and you'll see that each group row does  have a summary and it is colored just not always correctly.  

YES!! That fixes it.  Thanks so much Michael.