Reuse converters by chaining them together with a custom converter.

ValueConverterGroup.cs

public class ValueConverterGroup : List<IValueConverter>, IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        return this.Aggregate(value, (current, converter) => converter.Convert(current, targetType, parameter, culture));
    }

    public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        throw new NotImplementedException();
    }
}

XamlFile.xaml

<?xml version="1.0" encoding="utf-8" ?>
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             x:Class="someclass">
  <ContentPage.Resources>
    <ResourceDictionary>
      <!-- Converters -->
      <ValueConverterGroup x:Key="SelectionBackgroundColorConverter">
        <EqualsConverter></EqualsConverter>
        <BooleanToColorConverter TrueColor="{StaticResource GreenBackgroundColor}"
                                 FalseColor="{StaticResource GraySeperatorColor}"/>
      </ValueConverterGroup>
    </ResourceDictionary>
  </ContentPage.Resources>
</ContentPage>