ios swift uitextfielddelegate

Change custom text field background color and text color IOS Swift

I’m using following custom text field class to change appearance of the text field. Now I need to change text field’s background color, text color and place holder color, when user start editing and end editing the text field. How to do it, using this class.

import Foundation
import UIKit
class CustomTextField: UITextField{
required init(coder aDecoder: NSCoder) {
super.init(coder: aDecoder)
self.layer.cornerRadius = 15.0;
self.layer.borderWidth = 1.5
self.layer.borderColor = UIColor.whiteColor().CGColor
self.backgroundColor = UIColor(white: 1, alpha: 0.0)
self.textColor = UIColor.whiteColor()
self.textAlignment = NSTextAlignment.Center