title: Color Sets and UIColorAttributeTraitStorage error
body: <p>I've been trying to make an app written in Xcode 9 for iOS11 iOS9.0-compatible and all of a sudden it crashed with this error on iPhone 4S:</p>
  
  <pre><code>*** Terminating app due to uncaught exception 'NSInvalidUnarchiveOperationException', reason: 'Could not instantiate class named _UIColorAttributeTraitStorage'
  </code></pre>
  
  <p>Same project runs fine on iPhone 7. </p>
  
  <p>I've changed all [UIColor colorNamed:] as Xcode suggests:</p>
  
  <pre><code>if (@available(iOS 11.0, *)) {
          statusBar.backgroundColor = [UIColor colorNamed:@"MyColor"];
      } else {
          statusBar.backgroundColor = kColorFromHex(0x509E2F);
      }
  </code></pre>
  
  <p>But the error didn't go anywhere. I also didn't find any mention of UIColorAttributeTraitStorage in Apple Documentation or anywhere on the web except some japanese(?) <a href="http://www.jianshu.com/p/9bdcf2b278e4" rel="noreferrer">post</a>. All I understood from this post is that someone probably faced the same issue with Color Set in iOS 10.3 and Xcode 9. </p>
  
  <p>So it seems the problem is in xcassets containing Color Sets. Does this mean there is no backwards compatibility for Color Sets? And that if I add one there's no way to distribute my app for iOS lower than 11.0?</p>
  
  <p>P.S.: I don't have any iOS 10 device, so I don't know if the issue is still there for 10+ since Xcode 9 public release. Can anyone give it a try?</p>