title: Can't set @IBInspectable computed property in UIView
body: <p>I'm trying to add an <code>IBInspectable</code> color to UIView, so that I can set it in the storyboard and later use it in code. In <a href="https://stackoverflow.com/a/37416865/4502544">this post regarding UITextField</a> I've seen that I can take advantage of extensions and adding a computed property, but I can't make it work for UIView. </p>
  
  <p><a href="https://i.stack.imgur.com/y7Aov.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/y7Aov.png" alt="Identity inspector"></a>
  <a href="https://i.stack.imgur.com/U6fda.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/U6fda.png" alt="enter image description here"></a></p>
  
  <p>I get a crash: <em>Failed to set (additionalColor1) user defined inspected property on (UIView): [ setValue:forUndefinedKey:]: this class is not key value coding-compliant for the key additionalColor1.</em></p>
  
  <p>Any idea what's causing the crash and how to fix it?</p>
  
  <p>Here's my code:</p>
  
  <pre><code>extension UIView {
      @IBInspectable var additionalColor1: UIColor? {
          return self.additionalColor1
      }
  }
  </code></pre>
  
  <p>For the reference, I'm pasting the code that can be used to set the placeholder color for UITextField (same as the above url). This works ok:</p>
  
  <pre><code>extension UITextField {
      @IBInspectable var placeHolderColor: UIColor? {
          get {
              return self.placeHolderColor
          }
          set {
              self.attributedPlaceholder = NSAttributedString(string: self.placeholder != nil ? self.placeholder! : "", attributes:[NSForegroundColorAttributeName: newValue!])
          }
      }
  }
  </code></pre>