Change UITableViewCell's selectedBackgroundView color to transparent.
let clearView = UIView()
clearView.backgroundColor = UIColor.clearColor() // Whatever color you like
UITableViewCell.appearance().selectedBackgroundView = clearView
Here is the solution for swift 3,works even in editing mode
cell.selectionStyle = .gray
cell.selectedBackgroundView = {
let colorView = UIView()
colorView.backgroundColor = UIColor.black.withAlphaComponent(0.0)
//change the alpha value or color to match with you UI/UX
return colorView
}()