title: ARC forbids synthesizing a property with unspecified ownership or storage
body: <p>I've created a <code>@property</code> of <code>UIColor</code>,</p>
  
  <pre><code>@property (nonatomic) UIColor *color;
  </code></pre>
  
  <p>and then I tried to synthesize it:</p>
  
  <pre><code>@synthesize color = _color;
  </code></pre>
  
  <p>but I receive an error:</p>
  
  <blockquote>
    <p>ARC forbids synthesizing a property of Objective-C object with unspecified ownership or storage attribute</p>
  </blockquote>
  
  <p>What does that mean?</p>
  
  <p>All I'm trying to do is to create a property for a <code>UIColor</code> object which changes color.</p>