NotificationCenter

// ViewController class안에 생성
var someValue: Float = 0

// func 안에서 생성
NotificationCenter.default.post(name: NSNotification.Name.notiName, object: self)

// 파일명 : NotificationNameExtension.swift
extension Notification.Name {
    static let notiName = Notification.Name(rawValue: "notiNameValue")
}

// View func안에 생성
NotificationCenter.default.addObserver(forName: NSNotification.Name.notiName, object: nil, queue: OperationQueue.main) { (Notification) in
    let dataVC = Notification.object as! ViewController
    self.label.backgroundColor = UIColor(
        red: CGFloat(dataVC.redValue ),
        green: CGFloat(dataVC.greenValue),
        blue: CGFloat(dataVC.blueValue),
        alpha: CGFloat(dataVC.alphaValue))
}