title: Why isn't my UICollectionViewCell updating?
body: <p>I am checking to see if the indexPath of my cell is divisible by 7 when tapping on ti. If it is, the cell is supposed to change background colors. I believe my code is correct, but nothing is happening! </p>
  
  <pre><code>func collectionView(collectionView: UICollectionView, didSelectItemAtIndexPath indexPath: NSIndexPath) {
  
      let cell: CollectionViewCell = collectionView.dequeueReusableCellWithReuseIdentifier("cell", forIndexPath: indexPath) as! CollectionViewCell
  
      if (indexPath.row + 1) % 7 == 0 {
          print("true")
          cell.backgroundColor = UIColor(red: 70/255, green: 133/255, blue: 211/255, alpha:1.0)
      }
  
  }
  </code></pre>
  
  <p>I'm getting the true message, but the cell is not updating. Any idea why?</p>