How to customize the searchBar in a UISearchController?

set attributedPlaceholder for textfield of search bar

@IBOutlet weak var sbSearchBar: UISearchBar!
if let textfield = sbSearchBar.value(forKey: "searchField") as? UITextField {

    textfield.backgroundColor = UIColor.red
    textfield.attributedPlaceholder = NSAttributedString(string: textfield.placeholder ?? "", attributes: [NSAttributedStringKey.foregroundColor : UIColor.white])

    if let leftView = textfield.leftView as? UIImageView {
        leftView.image = leftView.image?.withRenderingMode(.alwaysTemplate)
        leftView.tintColor = UIColor.white
    }

}

Here is result:

Update:

I think, this may help you: how to change uitextfield color in searchcontroller?

Just apply your color combination in this code and see.

if #available(iOS 11.0, *) {
            let sc = UISearchController(searchResultsController: nil)
            sc.delegate = self
            let scb = sc.searchBar
            scb.tintColor = UIColor.white
            scb.barTintColor = UIColor.white


            if let textfield = scb.value(forKey: "searchField") as? UITextField {
                //textfield.textColor = // Set text color
                if let backgroundview = textfield.subviews.first {

                    // Background color
                    backgroundview.backgroundColor = UIColor.white

                    // Rounded corner
                    backgroundview.layer.cornerRadius = 10;
                    backgroundview.clipsToBounds = true;

                }
            }

            if let navigationbar = self.navigationController?.navigationBar {
                navigationbar.barTintColor = UIColor.blue
            }
            navigationItem.searchController = sc
            navigationItem.hidesSearchBarWhenScrolling = false

}

Result:

Add the following with your code in viewDidAppear:

            let placeholderString = NSAttributedString(string: "Placeholder", attributes: [NSAttributedStringKey.foregroundColor: UIColor.white])
            field.attributedPlaceholder = placeholderString

            let iconView = field.leftView as! UIImageView
            iconView.image = iconView.image?.withRenderingMode(.alwaysTemplate)
            iconView.tintColor = .white

Update - the following is the complete code to customize UISearchController colors:

override func viewDidAppear(_ animated: Bool) {

    //sets navigationbar backgroundColor
    if let navigationbar = self.navigationController?.navigationBar {
        navigationbar.barTintColor = UIColor.magenta
    }

    let searchField = searchController.searchBar.value(forKey: "searchField") as? UITextField

    //sets searchBar backgroundColor
    searchController.searchBar.backgroundColor = .blue

    if let field = searchField {
        field.layer.cornerRadius = 15.0
        //sets text Color
        field.textColor = .brown

        //sets indicator and cancel button Color
        field.tintColor = .green

        field.font = UIFont.systemFont(ofSize: 13)
        field.layer.masksToBounds = true
        field.returnKeyType = .search

        //sets placeholder text Color
        let placeholderString = NSAttributedString(string: "placeholder", attributes: [NSAttributedStringKey.foregroundColor: UIColor.red])
        field.attributedPlaceholder = placeholderString

        //sets icon Color
        let iconView = field.leftView as! UIImageView
        iconView.image = iconView.image?.withRenderingMode(.alwaysTemplate)
        iconView.tintColor = .cyan

        //sets textField backgroundColor
        if let backgroundview = field.subviews.first {
            backgroundview.backgroundColor = UIColor.yellow
        }
    }
}