How to display independent values in tooltip without changing the background color of pie chart using chartingtoolkit in xaml

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XAML

I have to display the independent values in the tooltip along with dependent values in pie chart but when i add the code mentioned below the background color gets changed to a single color. I want to display the piechart without effecting the default background color.

What I have tried:

<chartingToolkit:Chart  Name="PieChart1" Title="Department" Width="425" VerticalAlignment="Top" Margin="521,317,0,0" Height="262" HorizontalAlignment="Left">
               <chartingToolkit:PieSeries DependentValuePath="Value" IndependentValuePath="Key" ItemsSource="{Binding}" IsSelectionEnabled="True">
                   <chartingToolkit:PieSeries.DataPointStyle>
                       <Style TargetType="chartingToolkit:PieDataPoint">
                           <Setter Property="Template">
                               <Setter.Value>
                                   <ControlTemplate TargetType="chartingToolkit:PieDataPoint">
                                       <Grid>
                                           <Path Data="{TemplateBinding Geometry}"  Stroke="{TemplateBinding BorderBrush}"  StrokeMiterLimit="1" Fill="{TemplateBinding Background}">
                                               <ToolTipService.ToolTip>
                                                   <StackPanel>
                                                       <ContentControl Content="{Binding Key}"/>
                                                       <ContentControl Content="{TemplateBinding FormattedDependentValue}"/>
                                                       <ContentControl Content="{TemplateBinding FormattedRatio}"/>
                                                   </StackPanel>
                                               </ToolTipService.ToolTip>
                                           </Path>
                                       </Grid>
                                   </ControlTemplate>
                               </Setter.Value>
                           </Setter>
                       </Style>
                   </chartingToolkit:PieSeries.DataPointStyle>
               </chartingToolkit:PieSeries>
           </chartingToolkit:Chart>