public class ResourceConverter : IMultiValueConverter
{
  public object Convert(object[] values, Type targetType, object parameter, CultureInfo culture)
  {
    if (values.Length < 2) return DependencyProperty.UnsetValue;
    if (!(values[0] is FrameworkElement resOwner) || (values[1]==null)) return DependencyProperty.UnsetValue;
    var style = resOwner.TryFindResource(values[1].GetType()) as Style;
    if (style==null) return DependencyProperty.UnsetValue;
    foreach(var setter in style.Setters.OfType<Setter>())
      if (setter.Property.PropertyType == targetType)
        return setter.Value;
    return DependencyProperty.UnsetValue;
  }

  public object[] ConvertBack(object value, Type[] targetTypes, object parameter, CultureInfo culture)
  {
    throw new NotImplementedException();
  }
}

<ListBox DockPanel.Dock="Top" ItemsSource="{Binding ElementList}">
  <ListBox.ItemTemplate>
    <DataTemplate DataType="{x:Type system:String}">
      <Grid>
        <TextBlock Text="{Binding }">
          <TextBlock.Background>
            <MultiBinding Converter="{StaticResource ResourceConverter}">
              <Binding RelativeSource="{RelativeSource Mode=FindAncestor, AncestorType={x:Type DockPanel}}" />
              <Binding RelativeSource="{RelativeSource Self}" />
            </MultiBinding>
          </TextBlock.Background>
        </TextBlock>
      </Grid>
    </DataTemplate>
  </ListBox.ItemTemplate>
</ListBox>