title: ReactNative TextInput placeholderTextColor doesn't seem to be working
body: <p>It seems like such a simple thing, I don't see how I'm not getting this right, but <em>placeholderTextColor</em> on a ReactNative TextInput isn't doing anything for me. </p>
  
  <p><a href="http://facebook.github.io/react-native/docs/textinput.html#placeholdertextcolor" rel="noreferrer">http://facebook.github.io/react-native/docs/textinput.html#placeholdertextcolor</a></p>
  
  <pre><code>&lt;TextInput
      style={styles.input}
      placeholder="Foobar"
      placeholderTextColor="#FFFFFF"/&gt;
  </code></pre>
  
  <p>does nothing....</p>