Change UITextField's placeholder text colour

uitextfield-placeholder-color.swift

extension UITextField {
  public override func drawPlaceholderInRect(rect: CGRect) {
    let newColor = UIColor(white: 1, alpha: 0.4)
    let range = NSMakeRange(0, self.attributedPlaceholder!.length)
    
    var mutatedAttributedPlaceholder = NSMutableAttributedString(attributedString: self.attributedPlaceholder!)
    mutatedAttributedPlaceholder.setAttributes([ NSForegroundColorAttributeName : newColor ], range: range)
    self.attributedPlaceholder = mutatedAttributedPlaceholder
    
    super.drawPlaceholderInRect(rect)
  }
}