Replace UIRefreshControl with UIImageView

I have a UIRefreshControl in my UITableView. I want to replace the system's refresh icon with my own. I've tried just adding a subview to the refreshControl like so...

    let refreshImage = UIImageView()
    refreshImage.image = UIImage(named: "RefreshIcon")
    refreshControl.insertSubview(refreshImage, at: 0)
    tableview.addSubview(refreshControl)

But that did not work. Does anyone have any ideas? Thanks a lot!