SK3DNode unable to set scene's background color

I have this minimum reproducible code:

class GameViewController: UIViewController {
  
  override func viewDidLoad() {
    super.viewDidLoad()
    
    if let view = self.view as! SKView? {
      
      let scene = SKScene()
      let node3D = SK3DNode(viewportSize: CGSize(width: 200, height: 200))
      node3D.position = CGPoint(x: 100, y: 100)
      
      let scene3D = SCNScene()
      node3D.scnScene = scene3D
      scene.addChild(node3D)
      
      scene3D.background.contents = UIColor.red


      view.presentScene(scene)
      view.ignoresSiblingOrder = true
      view.showsFPS = true
      view.showsNodeCount = true
    }
  }
}

I set the background color for the scene kit content to be red, but the result is a dark color screen.

It is indeed strange, that UIColor.red is not working. Even CGColor is not working as expected. (According to the Documentation, it should work)

But here is, how you can fix the problem. I hope, it matches you requirements.

Scene Initialisation: Replace let scene = SKScene() with:

let scene = SKScene(size: view.bounds.size)

Background Color: Instead of using scene3D.background.contents = UIColor.red use a solid UIImage as the color source.

scene3D.background.contents = UIImage(color: .red)

In order to do so, you need to include this extension somewhere in your code. It will generate a UIImage with the given color:

extension UIImage {
    convenience init?(color: UIColor, size: CGSize = CGSize(width: 1, height: 1)) {
        UIGraphicsBeginImageContextWithOptions(size, false, 0)
        color.setFill()
        UIRectFill(CGRect(origin: .zero, size: size))
        let image = UIGraphicsGetImageFromCurrentImageContext()
        UIGraphicsEndImageContext()
        
        guard let cgImage = image?.cgImage else { return nil }
        self.init(cgImage: cgImage)
    }
}

Result: (scroll down)