无法使用if condition Swift 4.0更改文本颜色

import UIKit

class ViewController: UIViewController {
    @IBOutlet weak var label: UILabel!
    
    var isConditionMet: Bool = false {
        didSet {
            if isConditionMet {
                label.textColor = .green
            } else {
                label.textColor = .red
            }
        }
    }
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        // 设置初始文本颜色
        label.textColor = .red
        
        // 模拟条件变化
        isConditionMet = true
    }
}