How to get cell atIndex in UICollectionView with swift?

In Swift 4 you can get the cell of CollectionView with:

let indexPath = IndexPath(item: 3, section: 0);  
if let cell = myCollectionView .cellForItem(at: indexPath)  
{   
   // do stuff...  
}  

This is the way to get the cell at a given indexPath:

let cell = collectionView!.cellForItemAtIndexPath(indexPath)

However, you also might want to try:

cell.contentView.backgroundColor = UIColor.blueColor()

NOTE:

Though the above may have worked, I want to encourage you to try a different implementation to achieve the same functionality. Your implementation would require you to have a separate Action# function for each CollectionViewCell, as well as create the indexPath manually in each of those methods, when you could potentially only have one!

func collectionView(collectionView: UICollectionView, cellForItemAtIndexPath indexPath: NSIndexPath) -> UICollectionViewCell {
    let cell = collectionView.dequeueReusableCellWithReuseIdentifier("CollectionViewCell", forIndexPath: indexPath) as! CollectionViewCell
    cell.backgroundColor = UIColor.blackColor()
    cell.buttonView.addTarget(self, action: Selector("action"), forControlEvents: UIControlEvents.TouchUpInside)
    return cell
}

and the function for that one method would be something like:

func action(sender: UIButton!) {
    var point : CGPoint = sender.convertPoint(CGPointZero, toView:collectionView)
    var indexPath = collectionView!.indexPathForItemAtPoint(point)
    let cell = collectionView!.cellForItemAtIndexPath(indexPath)
    cell.backgroundColor = UIColor.blueColor()
}

Updated action function for Swift 4.2

@objc func action(sender: Any){
    print("tickedOffPressed !")
    if let button = sender as? UIButton {
        let point: CGPoint = button.convert(.zero, to: collectionView)
        if let indexPath = collectionView!.indexPathForItem(at: point) {
            let cell = collectionView!.cellForItem(at: indexPath)
            cell?.backgroundColor = UIColor.blue
        }
    }
}

Just a suggestion! Happy coding! :)