title: a black image's color can not be changed in Unity
body: <p>the color of a black image , or the black part of a image, can not be changed.
  <img src="https://i.stack.imgur.com/1194W.png" alt="example"></p>
  
  <p>I set the image's color to red, but the image is still black.</p>
  
  <p>Is that a desired feature?</p>
  
  <p>What i want is , the image is changed to red.</p>
  
  <p>the Unity version is 5.0.1f.
  I am using the new UI.</p>