Swift 如何从UIKit中的AttributeContainer获取属性并将其分配给某个变量

我创建下一个子类:

import UIKit

class Button: UIButton {

    override func updateConfiguration() {
        var config = configuration ?? UIButton.Configuration.plain()

        let color = config.attributedTitle?.foregroundColor

        switch state {
        case .normal:
            config.attributedTitle?.foregroundColor = color.withAlphaComponent(1)

        case .highlighted:
            config.attributedTitle?.foregroundColor = color.withAlphaComponent(0.5)

        default:
            break
        }

        configuration = config
    }
}

I this class I want to get foregroundColor from attributedTittle(AttributedString class) to assign it later with alphaComponent to different button states, BUT I can't get any attribute from attributedString(or AttributedContainer) in updateConfiguration method.
In my example property "color" is always nil (actually all other attribute are nil if I try get them) and the return type of "color" is:

AttributeScopes.SwiftUIAttributes.ForegroundColorAttribute.Value?

在try 将 colored颜色 重新分配给属性字符串时，我收到以下错误:

 Value of type 'AttributeScopes.SwiftUIAttributes.ForegroundColorAttribute.Value?' (aka 'Optional<Color>') has no member 'withAlphaComponent'

那么，为什么我在这里无法从AttributedString获取任何属性呢？