X.SetResourceReference(Shape.FillProperty, "XHighlightBorderBrush");

public static void SetDynamicResourceKey( DependencyObject obj, DependencyProperty prop, object resourceKey)
        {
            var dynamicResource = new DynamicResourceExtension(resourceKey);
            var resourceReferenceExpression = dynamicResource.ProvideValue(null);
            obj.SetValue(prop, resourceReferenceExpression);
        }