Use UIColorPickerViewController to pick color from the selected image

UIColorPickerViewControllerDemo.swift

class ViewController: UIViewController {

  private let imagePicker = UIImagePickerController()
  private let colorPicker = UIColorPickerViewController()
  private let imageView = UIImageView(image: nil)
  private let colorView = UIView()
  private let isSetUp = false

  override func viewDidLayoutSubviews() {
    if !isSetUp {
      setUp()
    }
  }

  private func setUp() {
    let insets = view.safeAreaInsets
    let toolBar = UIToolbar()
    toolBar.frame = CGRect(x: 0, y: insets.top, width: view.bounds.width, height: 44)
    toolBar.items = [
      UIBarButtonItem(title: "Photo", style: .plain, target: self, action: #selector(openImagePicker)),
      UIBarButtonItem(barButtonSystemItem: .flexibleSpace, target: nil, action: nil),
      UIBarButtonItem(title: "Color Picker", style: .plain, target: self, action: #selector(openColorPicker)),
    ]
    view.addSubview(toolBar)

    imagePicker.delegate = self
    imagePicker.mediaTypes = ["public.image"]
    imagePicker.sourceType = .photoLibrary

    colorPicker.supportsAlpha = true
    colorPicker.selectedColor = UIColor.blue
    colorPicker.delegate = self

    let contentFrame = CGRect(x: 0, y: toolBar.frame.maxY, width: view.bounds.width, height: view.bounds.height - insets.bottom)
    let (slice, remainder) = contentFrame.divided(atDistance: view.bounds.width, from: .minYEdge)

    imageView.frame = slice
    imageView.contentMode = .scaleAspectFill
    view.addSubview(imageView)

    colorView.frame = remainder
    view.addSubview(colorView)

    colorView.backgroundColor = .black
    imageView.backgroundColor = .darkGray
    view.backgroundColor = .white
  }

  @objc func openImagePicker() {
    present(imagePicker, animated: true)
  }

  @objc func openColorPicker() {
    present(colorPicker, animated: true, completion: nil)
  }
}

extension ViewController: UIImagePickerControllerDelegate, UINavigationControllerDelegate {
  func imagePickerController(_ picker: UIImagePickerController, didFinishPickingMediaWithInfo info: [UIImagePickerController.InfoKey: Any]) {
    imageView.image = info[.originalImage] as? UIImage
    picker.dismiss(animated: true, completion: nil)
  }
}

extension ViewController: UIColorPickerViewControllerDelegate {
  func colorPickerViewControllerDidSelectColor(_ viewController: UIColorPickerViewController) {
    colorView.backgroundColor = viewController.selectedColor
  }

  func colorPickerViewControllerDidFinish(_ viewController: UIColorPickerViewController) {
    viewController.dismiss(animated: true, completion: nil)
  }
}