title: Fix UIVisualEffectView extra light blur being gray on white background
body: <p>Apple provides this live blurring view class <a href="https://developer.apple.com/library/ios/documentation/UIKit/Reference/UIVisualEffectView/" rel="noreferrer"><code>UIVisualEffectView</code></a> and you use it with a <a href="https://developer.apple.com/library/ios/documentation/UIKit/Reference/UIBlurEffect_Ref/index.html#//apple_ref/occ/cl/UIBlurEffect" rel="noreferrer"><code>UIBlurEffect</code></a> which takes one of three available <a href="https://developer.apple.com/library/ios/documentation/UIKit/Reference/UIBlurEffect_Ref/index.html#//apple_ref/c/tdef/UIBlurEffectStyle" rel="noreferrer"><code>UIBlurEffectStyle</code>s</a>:</p>
  
  <pre><code>enum UIBlurEffectStyle : Int {
      case ExtraLight
      case Light
      case Dark
  }
  </code></pre>
  
  <p>Now for demo purposes I set up two effect views with the styles <code>Light</code> and <code>ExtraLight</code>:</p>
  
  <pre><code>let lightBlur = UIBlurEffect(style: UIBlurEffectStyle.Light)
  let extraLightBlur = UIBlurEffect(style: UIBlurEffectStyle.ExtraLight)
  
  let lightView = UIVisualEffectView(effect: lightBlur)
  lightView.frame = CGRectMake(10, 30, 150, 150)
  self.view.addSubview(lightView)
  
  let extraLightView = UIVisualEffectView(effect: extraLightBlur)
  extraLightView.frame = CGRectMake(160, 30, 150, 150)
  self.view.addSubview(extraLightView)
  </code></pre>
  
  <p>So far so good, everything works as expected, they blur images:</p>
  
  <p><a href="https://i.stack.imgur.com/2oIES.png" rel="noreferrer"><img src="https://i.stack.imgur.com/2oIES.png" alt="image"></a></p>
  
  <p>and kind of work on colors, too:</p>
  
  <p><a href="https://i.stack.imgur.com/kO6eI.png" rel="noreferrer"><img src="https://i.stack.imgur.com/kO6eI.png" alt="black"></a>
  <a href="https://i.stack.imgur.com/NhGsI.png" rel="noreferrer"><img src="https://i.stack.imgur.com/NhGsI.png" alt="red"></a></p>
  
  <p>but when it comes to a white background this happens:</p>
  
  <p><a href="https://i.stack.imgur.com/GEksy.png" rel="noreferrer"><img src="https://i.stack.imgur.com/GEksy.png" alt="white"></a></p>
  
  <p>The <code>Light</code> effect on the left works as expected, but the <code>ExtraLight</code> effect on the right leaves some kind of gray square behind.</p>
  
  <p>Now the question: Is there any kind of trick or method that would enable me to use an extra light blur effect on white background (with live blurring support) AND remove that ugly gray shadow?</p>