title: iOS: In `UIScrollView`'s delegate,I want to change `grey color` to `green color` by gradual changing
body: <p>I have tried in my code to gradual change <code>textColor</code> in <code>UIScrollView</code>'s delegate:</p>
  
  <pre><code>- (void)scrollViewDidScroll:(UIScrollView *)scrollView
  {
  
      CGFloat rightScale = scrollView.contentOffset.x / [UIScreen mainScreen].bounds.size.width;
      //  0~1
      rightScale = rightScale - leftI;
  
      CGFloat leftScale = 1 - rightScale;
  
      // #define APP_COLOR RGB(30, 170, 61)
      [leftLabel setTextColor:kColor( leftScale * 30 / 255.0 , leftScale *170 / 255.0,  leftScale *61 / 255.0)];
      [rigthLabel setTextColor:kColor(rightScale * 30 / 255.0, rightScale * 170 / 255.0, rightScale  * 61 / 255.0)];
  }
  </code></pre>
  
  <p>In the result I can only change <code>black color</code> to my <code>APP_COLOR</code>, but I want to change a <code>custom color</code> to <code>APP_COLOR</code>,I don't know the answer off the top of my stupid head.</p>