title: insertSublayer atIndex puts things on top of other layers
body: <p>I'm using ColorBGView and calling methods inside of it to make gradients. But if I attach two to my layer, it overlaps everything else I attach afterward, and I don't understand why.</p>
  
  <pre><code>        CAGradientLayer *bgLayer = [ColorBGView pinkSky1];
          bgLayer.frame = CGRectMake(0, 0, 1024, 768);
          [viewController.view.layer insertSublayer:bgLayer atIndex:0];
  
      //If I insert this sublayer (even at a lower index) 
      //it overlaps everything I attach afterward
  
          CAGradientLayer *bgLayer2 = [ColorBGView darkCave];
          bgLayer2.frame = CGRectMake(0, 0, 1024, 768);
          [viewController.view.layer insertSublayer:bgLayer2 atIndex:-10];    
  
          // add custom view
  
          parallaxView = [[ParallaxView alloc] init];
          parallaxView.frame = CGRectMake(0, 0, 1024, 768);
          [viewController.view insertSubview:parallaxView atIndex:1];
  
          [parallaxView release];
  </code></pre>