<UserControl.Resources>
    <ResourceDictionary>
        <CollectionViewSource x:Key="filteredSymbols" Source="{Binding Symbols ,RelativeSource={RelativeSource AncestorType=UserControl}}"
                              Filter="Symbols_CollectionViewSource_Filter" IsLiveFilteringRequested="True" >
            <CollectionViewSource.LiveFilteringProperties>
                <sys:String>DisplayPage</sys:String>
            </CollectionViewSource.LiveFilteringProperties>
        </CollectionViewSource>
    </ResourceDictionary>
</UserControl.Resources>

...

<Border Background="{Binding Source={StaticResource filteredSymbols}, Converter={StaticResource MultiThresholdToReturnValueConverter}}" >