Simple Animations

UIView.animate(withDuration: 1) { 
    self.view.backgroundColor = UIColor.darkGray
}

And when you need a delay:

UIView.animate(withDuration: 4, delay: 5, options: [], animations: {
    self.view.backgroundColor = UIColor.darkGray
}, completion: nil)

What can be animated?

Here are some common properties (but not all):

• UIView.alpha - Use this to fade objects in or out. (Adjusts transparency)
• UIView.bounds - Defines the X,Y position of self (0,0) and the width, height of the object. Use to change the object's size or even position.
• UIView.center - Use to change the position of the object on the screen.
• UIView.frame - Defines the X,Y position inside its parent and the width, height of the object. Reposition or resize within a parent view.
• UIView.transform - Use this to rotate, scale, translate and skew objects.
• UIColor - Such as text color or background color. You can animate changing color such as in the example above.
• view.layoutIfNeeded() - Make changes to an object's constants and then call this function inside the animations block to see those changes animate.

(Swift 3)