UICollectionView Cell with Image, change Backgroun

I have a Collection View that looks like this:

The blue border is an image. When I press them I want the text and the image to dim briefly.

I found this SO question that is similar:

UICollectionView Cell with Image, change Background with click

And it included this answer in Objective-C:

If you have a CustomCell, you must have a CustomCell.m (implementation file). In this file add this, to me is the easy way:
-(void)setHighlighted:(BOOL)highlighted
{
    if (highlighted)
    {
        self.layer.opacity = 0.6;
        // Here what do you want.
    }
    else{
        self.layer.opacity = 1.0;
        // Here all change need go back
    }
}

I tried adding this to my custom UICollectionViewCell like this:

import UIKit

class DoubleSoundsCollectionViewCell: UICollectionViewCell {

    @IBOutlet weak var cellLabel: UILabel!

    func highlighted(highlighted: Bool) {
        if (highlighted)
        {
            self.layer.opacity = 0.6;
            // Here what do you want.
        }
        else{
            self.layer.opacity = 1.0;
            // Here all change need go back
        }
    }
}

But there was no noticeable effect on my collection view when I tap a cell. Did I add it in the wrong place or did I convert it to Swift in the wrong way?

If I call the method setHighlighed, then I get the error

[PATH]/DoubleSoundsCollectionViewCell.swift:15:10: Method 'setHighlighted' with Objective-C selector 'setHighlighted:' conflicts with setter for 'highlighted' from superclass 'UICollectionViewCell' with the same Objective-C selector

Because highlighted is a property in Swift.

See UICollectionViewCell declaration in Swift.

public var highlighted: Bool

So you will need to override the property like this.

class DoubleSoundsCollectionViewCell : UICollectionViewCell {

    override var highlighted: Bool {
        didSet {
            // add your implementation here
        }
    }
}

You should always know in Swift. You have to include override keyword if you are overriding something, if the compiler accept it without override, then you are doing something wrong.