WPF

<ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="clr-namespace:WpfApplication1">
    <Style TargetType="Button">
        <Setter Property="Button.Template">
            <Setter.Value>
                <ControlTemplate>
                    <Grid>
                        <local:StyleChangedControl x:Name="MyStyleChangeCon" />
                        <Rectangle>
                            <Rectangle.Fill>
                                <SolidColorBrush x:Name="rectFill" Color="Yellow" />
                            </Rectangle.Fill>
                        </Rectangle>
                        <ContentPresenter Content="{TemplateBinding Button.Content}" />
                    </Grid>
                    <ControlTemplate.Triggers>
                        <EventTrigger SourceName="MyStyleChangeCon" RoutedEvent="local:StyleChangedControl.StyleChange">
                            <BeginStoryboard>
                                <Storyboard>
                                    <ColorAnimation
                                        Storyboard.TargetName="rectFill"
                                        Storyboard.TargetProperty="Color"
                                        To="Blue"
                                        AutoReverse="True"
                                        RepeatBehavior="Forever"
                                        Duration="0:0:1" />
                                </Storyboard>
                            </BeginStoryboard>
                        </EventTrigger>
                    </ControlTemplate.Triggers>
                </ControlTemplate>
            </Setter.Value>
        </Setter>
    </Style>
</ResourceDictionary>

<Window x:Class="WpfApplication1.Window1"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="Window1" Height="300" Width="300">
    <Button Click="Button_Click">Change Style</Button>
</Window>

// Main window.
public partial class Window1 : Window
{

	// Constructor.
	public Window1() {InitializeComponent();}

	// This button event changes the style.
	private void Button_Click(object sender, RoutedEventArgs e)
	{

		// Assign the new style.
		Application.Current.Resources.MergedDictionaries.Add(
			(ResourceDictionary)Application.LoadComponent(
			new Uri(@"AnimatedStyleDictionary.xaml", UriKind.Relative)));
		
		// Queue up a thread so the above style gets a
		// chance to apply before the below code executes.
		Thread t = new Thread(new ThreadStart(delegate()
		{
			this.Dispatcher.Invoke(new ThreadStart(delegate()
			{
				// Send notification that application style changed.
				StyleChangedControl.NotifyOfApplicationStyleChange();
			}));
		}));
		t.Start();

	}

}

// The sole purpose of this control is to fire the StyleChange event.
public class StyleChangedControl : Control
{

	// The static event.
	private static event ThreadStart ApplicationStyleChange;

	// The event that is on every instance of StyleChangedControl.
	public event RoutedEventHandler StyleChange
	{
		add
		{
			AddHandler(StyleChangeEvent, value);
		}
		remove
		{
			RemoveHandler(StyleChangeEvent, value);
		}
	}
	public static RoutedEvent StyleChangeEvent =
		EventManager.RegisterRoutedEvent("StyleChange",
		RoutingStrategy.Direct, typeof(RoutedEventHandler),
		typeof(StyleChangedControl));

	// Other classes call this when they change the application style.
	public static void NotifyOfApplicationStyleChange()
	{
		if (ApplicationStyleChange != null)
		{
			// Notify instances of style change.
			ApplicationStyleChange();
		}
	}

	// Constructor.
	public StyleChangedControl()
	{

		// This control does not need to be seen.
		this.Visibility = Visibility.Collapsed;

		// Subscribe instance method to static event.
		ApplicationStyleChange += this.OnStyleChange;

	}

	// Static event calls this.
	private void OnStyleChange()
	{

		// Raise event to notify all listening EventTriggers.
		RoutedEventArgs e = new RoutedEventArgs(StyleChangeEvent);
		RaiseEvent(e);

	}

}

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</Expander>