title: Why is CGImageCreateWithMaskingColors() returning nil in this case?
body: <p>When I use the following code:</p>
  
  <pre><code>UIImage *image=[UIImage imageNamed:@"loginf1.png"];
  CGImageRef rawImageRef=image.CGImage;
  
  const float colorMasking[6] = {222, 255, 222, 255, 222, 255};
  
  CGImageRef maskedImageRef=CGImageCreateWithMaskingColors(rawImageRef, colorMasking);
  </code></pre>
  
  <p><code>maskedImageRef</code>is always nil.  Why is this, and what can I do to correct this?</p>