title: UIKit. How to set Transparent color?
body: <p>Is there any way to set any color of UIImage (or it CALayer content) as transparent color?</p>
  
  <p>I cannot use single image resource(PNG file) with built-in transparency. <br/> </p>
  
  <p>I need to hide some area from first Layer by overlaying second Layer with specific color at that place. So I need to set this specific color as "transparent color" before assembled image drawing. </p>
  
  <p>Image area I need to hide is like background - <strong>i.e. specific color will be started from image borders through whole perimeter.</strong> </p>