Вы можете попробовать это
UITextField.appearance(whenContainedInInstancesOf: [type(of: searchController.searchBar)]).backgroundColor = .yellow
UITextField.appearance(whenContainedInInstancesOf: [type(of: searchController.searchBar)]).tintColor = .blue
Выход
Редактировать: ПолныйКод
var searchController = UISearchController()
let resultsTableController = Storyboard.Home.instantiateViewController(withIdentifier: "GlobalTableVC") as! GlobalTableVC
resultsTableController.tableView.delegate = self
resultsTableController.tableView.dataSource = self
resultsTableController.tableView.register(UITableViewCell.self, forCellReuseIdentifier: "SearchCell")
searchController = UISearchController(searchResultsController: resultsTableController)
searchController.searchBar.placeholder = "Search"
searchController.dimsBackgroundDuringPresentation = true
searchController.searchBar.sizeToFit()
searchController.hidesNavigationBarDuringPresentation = false
searchController.searchBar.keyboardType = UIKeyboardType.alphabet
searchController.searchBar.tintColor = UIColor.white
searchController.searchBar.barTintColor = UIColor(hexString: "EB033B")
UITextField.appearance(whenContainedInInstancesOf: [type(of: searchController.searchBar)]).backgroundColor = .yellow
UITextField.appearance(whenContainedInInstancesOf: [type(of: searchController.searchBar)]).tintColor = .blue
searchController.searchBar.delegate = self
searchController.delegate = self
searchController.searchResultsUpdater = self
present(searchController, animated: true, completion: nil)