<?xml version="1.0" encoding="utf-8"?>
<s:SparkSkin 
	
	xmlns:s="library://ns.adobe.com/flex/spark" 
	xmlns:fx="http://ns.adobe.com/mxml/2009" 
	xmlns:d="http://ns.adobe.com/fxg/2008/dt" 
	xmlns:ai="http://ns.adobe.com/ai/2008"
	
	horizontalCenter="{width/2}"
	verticalCenter="{height/2}"
	>
	
	<fx:Metadata>[HostComponent("spark.components.Button")]</fx:Metadata>
	
	<fx:Declarations>
		
		<fx:Vector
			id="alphaInVector"
			type="spark.effects.animation.MotionPath"
			>
			<s:SimpleMotionPath
				
				property="alpha"
				valueFrom="0"
				valueTo="1"
				/>
		</fx:Vector>
		
		<s:GlowFilter
			
			id="glowFilter"
			inner="true"
			
			strength.up="0"
			strength.over="2"
			strength.down="2"
			
			blurX="{width/4}"
			blurY="{height/4}"
			
			color="0x009900"
			/>
		
	</fx:Declarations>
	
	<s:transitions>
		<s:Transition fromState="*" toState="*">
			<s:AnimateFilter 
				
				bitmapFilter="{glowFilter}"
				target="{circle}" 
				motionPaths="{alphaInVector}" 
				repeatBehavior="reverse" 
				repeatCount="0" 
				/>
		</s:Transition>
	</s:transitions>
	
	<s:states>
		<s:State name="up"/>
		<s:State name="over"/>
		<s:State name="down"/>
		<s:State name="disabled"/>
	</s:states>
	
	<s:Ellipse 
		
		id="circle"
		left="0" right="0" top="0" bottom="0"
		>
		<s:fill>
			<s:SolidColor color="{getStyle('color')}" alpha="{getStyle('backgroundAlpha')}"/>
		</s:fill>
	</s:Ellipse>
	
	<s:Label
		
		text="{hostComponent.label}"
		fontFamily="Arial" 
		fontSize="14"
		color="0xffffff" 
		color.disabled="888888"
		horizontalCenter="0" 
		verticalCenter="0"
		left="2" 
		right="2" 
		top="4" 
		bottom="2"
		textAlign="center" 
		verticalAlign="middle"
		/>
	
</s:SparkSkin>

SparkSkin with animated filter

MXML