UITableViewCell Selected Background Color on Multiple Selection

All the above answers are fine but a bit to complex to my liking. The simplest way to do it is to put some code in the cellForRowAtIndexPath. That way you never have to worry about changing the color when the cell is deselected.

override func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {
    let cell = tableView.dequeueReusableCellWithIdentifier("cell", forIndexPath: indexPath)

    /* this is where the magic happens, create a UIView and set its
       backgroundColor to what ever color you like then set the cell's
       selectedBackgroundView to your created View */

    let backgroundView = UIView()
    backgroundView.backgroundColor = YOUR_COLOR_HERE
    cell.selectedBackgroundView = backgroundView
    return cell
}