Extension to provide an equivalent opaque UIColor to a UIColor with alpha channel. So: f(r,g,b,a) == (r,g,b,1)

opaqueEquivalent.swift

import UIKit

public extension UIColor {

  var components: (red: CGFloat, green: CGFloat, blue: CGFloat, alpha: CGFloat) {
      var red: CGFloat = 0
      var green: CGFloat = 0
      var blue: CGFloat = 0
      var alpha: CGFloat = 0

      getRed(&red, green: &green, blue: &blue, alpha: &alpha)

      return (red, green, blue, alpha)
  }

  func opaqueEquivalent(withBackground color: UIColor = .white) -> UIColor {

    let bColor = color.components
    let fColor = components
    let alpha = fColor.alpha


    func finalChannel(_ fColor: CGFloat, _ bColor: CGFloat) -> CGFloat {
      (1 - alpha) * bColor + (fColor * alpha)
    }

    let newRed = finalChannel(fColor.red, bColor.red)
    let newGreen = finalChannel(fColor.green, bColor.green)
    let newBlue = finalChannel(fColor.blue, bColor.blue)

    return UIColor(red: newRed, green: newGreen, blue: newBlue, alpha: 1.0)
  }
}