     self.init(red: red, green: green, blue: blue, alpha: alpha)
   }
   
+  /// Create a black or white UIColor object that constrasts to specified color.
+  /// - Parameter backgroundColor: specified color
   convenience init(constrastingBlackOrWhiteColorOn backgroundColor: UIColor) {
     let rgba = backgroundColor.rgbaComponents
     

    self.init(red: CGFloat(red) / 255.0, green: CGFloat(green) / 255.0, blue: CGFloat(blue) / 255.0, alpha: alpha)
  }
  
  convenience init(hexString: String, alpha: CGFloat = 1) {
    let string = hexString.trimmingCharacters(in: .whitespacesAndNewlines).uppercased()
    let scanner = Scanner(string: string)

import UIKit

public extension UIColor {
  
  /// Return a random color
  static var random: UIColor {
    let red = (0...255).randomElement()!
    let green = (0...255).randomElement()!
