如何在索引的UITableView中更改侧面Alphabet的颜色？

import UIKit

class CustomTableView: UITableView {
    override func layoutSubviews() {
        super.layoutSubviews()
        
        for subview in subviews {
            if let indexView = subview as? UIIndexView {
                indexView.tintColor = UIColor.red
            }
        }
    }
}

class ViewController: UIViewController, UITableViewDataSource, UITableViewDelegate {
    @IBOutlet weak var tableView: CustomTableView!
    
    let sections = ["A", "B", "C", "D", "E", "F", "G", "H", "I", "J", "K", "L", "M", "N", "O", "P", "Q", "R", "S", "T", "U", "V", "W", "X", "Y", "Z"]
    
    override func viewDidLoad() {
        super.viewDidLoad()
        tableView.dataSource = self
        tableView.delegate = self
    }
    
    // MARK: - UITableViewDataSource
    
    func numberOfSections(in tableView: UITableView) -> Int {
        return sections.count
    }
    
    func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
        return 1
    }
    
    func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
        let cell = tableView.dequeueReusableCell(withIdentifier: "Cell", for: indexPath)
        cell.textLabel?.text = "Section \(sections[indexPath.section])"
        return cell
    }
    
    // MARK: - UITableViewDelegate
    
    func sectionIndexTitles(for tableView: UITableView) -> [String]? {
        return sections
    }
    
    func tableView(_ tableView: UITableView, sectionForSectionIndexTitle title: String, at index: Int) -> Int {
        return index
    }
}