public static void showSnapshot() {
		if( !FlatSystemProperties.getBoolean( "flatlaf.animatedLafChange", true ) )
			return;

		// stop already running animation
		if( animator != null )
			animator.stop();

		alpha = 1;

		// show snapshot of old UI
		showSnapshot( true, oldUIsnapshots );
	}
Create a snapshot of the old UI and shows it on top of the UI.
Invoke before setting new look and feel.
flatlaf-extras/src/main/java/com/formdev/flatlaf/extras/FlatAnimatedLafChange.java