UIButton+BackgroundState.swift

extension UIButton {
    // https://stackoverflow.com/questions/14523348/how-to-change-the-background-color-of-a-uibutton-while-its-highlighted
    private func image(withColor color: UIColor) -> UIImage? {
        let rect = CGRect(x: 0.0, y: 0.0, width: 1.0, height: 1.0)
        UIGraphicsBeginImageContext(rect.size)
        let context = UIGraphicsGetCurrentContext()
        
        context?.setFillColor(color.cgColor)
        context?.fill(rect)
        
        let image = UIGraphicsGetImageFromCurrentImageContext()
        UIGraphicsEndImageContext()
        
        return image
    }
    
    func setBackgroundColor(_ color: UIColor, for state: UIControlState) {
        self.setBackgroundImage(image(withColor: color), for: state)
    }
}