title: iOS 13 `withTintColor` not obeying the color I assign
body: <p>I find the behavior of the new iOS 13 UIImage property <code>withTintColor(_:renderingMode:)</code> incomprehensible. What is it for, and how does it relate to the tint color of the context in which the image appears?</p>
  
  <p>For example:</p>
  
  <pre><code>let im = UIImage(systemName:"circle.fill")?.withTintColor(.red)
  let iv = UIImageView(image:im)
  iv.frame.origin = CGPoint(x: 100, y: 400)
  self.view.addSubview(iv)
  </code></pre>
  
  <p>I said <code>.red</code>. But it's blue:</p>
  
  <p><a href="https://i.stack.imgur.com/t7jnM.png" rel="noreferrer"><img src="https://i.stack.imgur.com/t7jnM.png" alt="enter image description here"></a></p>
  
  <p>Evidently it's blue because it takes its color from the tint color of the surrounding context. But then what's the point of giving the image <em>itself</em> a tint color?</p>
  
  <p>But it gets even weirder. I'll draw my own image and give <em>it</em> a tint color:</p>
  
  <pre><code>let sz = CGSize(width: 20, height: 20)
  let im = UIGraphicsImageRenderer(size:sz).image { ctx in
      ctx.cgContext.fillEllipse(in:CGRect(origin:.zero, size:sz))
  }.withTintColor(.red)
  let iv = UIImageView(image:im)
  iv.frame.origin = CGPoint(x: 100, y: 400)
  self.view.addSubview(iv)
  </code></pre>
  
  <p>I said <code>.red</code> and it's red:</p>
  
  <p><a href="https://i.stack.imgur.com/a5MY7.png" rel="noreferrer"><img src="https://i.stack.imgur.com/a5MY7.png" alt="enter image description here"></a></p>
  
  <p>What accounts for the inconsistency?</p>