title: Cannot change UIBarButtonItem color attribute in disabled state
body: <p>I have created a UIToolBar with three bar button items.  All works well when using the default font and font size.  However, the font is a bit too large and I want to resize it.  I used the following code to successfully customize the font size and color in the normal state, but when, say, button #1 is disabled  the text color remains black for both the enabled and disabled states  - i.e. it doesn't change color to gray.</p>
  
  <pre><code>NSDictionary *ena = @{NSFontAttributeName:[UIFont fontWithName:@"Helvetica" size:12.0], NSForegroundColorAttributeName:
                             [UIColor blackColor]};
  NSDictionary *dis = @{NSFontAttributeName:[UIFont fontWithName:@"Helvetica" size:12.0], NSForegroundColorAttributeName:
                              [UIColor grayColor]};
  
  [[UIBarButtonItem appearance] setTitleTextAttributes:ena forState:UIControlStateNormal];
  [[UIBarButtonItem appearance] setTitleTextAttributes:dis forState:UIControlStateDisabled];
  </code></pre>
  
  <p>I'd appreciate some feedback on where I went wrong with the above code.</p>