How do I save a UIColor with UserDefaults?

I'm trying to program my code so that if the user presses the Night Button the background will turn black and stay black if the user closes the app. (Same goes for day mode.)

Please note: I already coded buttons and when they press it, all of the scenes change to that mode.

Here's my code where I'm going going to need the background color to be saved: (I need it in both if statements)

if GlobalData.dayBool == true && GlobalData.night == false {
    backgroundColor = GlobalData.dayColor 
}

if GlobalData.nightBool == true && GlobalData.dayBool == false {
    backgroundColor = GlobalData.nightColor 
}

My Night and Day Colors:

struct GlobalData {
    static var score = 0
    static var dayColor = UIColor(red:0.93, green:0.93, blue:0.93, alpha:1.0)
    static var nightColor = UIColor(red:0.10, green:0.10, blue:0.10, alpha:1.0)  
    static var dayBool = true
    static var nightBool = true
}

Swift 5.2 or later

Note that this will save only the RGBA CGFloat values as Data inside the property list. This will use 32 bytes (raw data) instead of 424 bytes needed when using the standard approach with NSKeyedUnarchiver (NSCoding):

extension Numeric {
    var data: Data {
        var bytes = self
        return Data(bytes: &bytes, count: MemoryLayout<Self>.size)
    }
}

extension Data {
    func object<T>() -> T { withUnsafeBytes{$0.load(as: T.self)} }
    var color: UIColor { .init(data: self) }
}

extension UIColor {
    convenience init(data: Data) {
        let size = MemoryLayout<CGFloat>.size
        self.init(red:   data.subdata(in: size*0..<size*1).object(),
                  green: data.subdata(in: size*1..<size*2).object(),
                  blue:  data.subdata(in: size*2..<size*3).object(),
                  alpha: data.subdata(in: size*3..<size*4).object())
    }
    var rgba: (red: CGFloat, green: CGFloat, blue: CGFloat, alpha: CGFloat)? {
        var (red, green, blue, alpha): (CGFloat, CGFloat, CGFloat, CGFloat) = (0, 0, 0, 0)
        return getRed(&red, green: &green, blue: &blue, alpha: &alpha) ?
        (red, green, blue, alpha) : nil
    }
    var data: Data? {
        guard let rgba = rgba else { return nil }
        return rgba.red.data + rgba.green.data + rgba.blue.data + rgba.alpha.data
    }
}

extension UserDefaults {
    func set(_ color: UIColor?, forKey defaultName: String) {
        guard let data = color?.data else {
            removeObject(forKey: defaultName)
            return
        }
        set(data, forKey: defaultName)
    }
    func color(forKey defaultName: String) -> UIColor? {
        data(forKey: defaultName)?.color
    }
}

extension UserDefaults {
    var backgroundColor: UIColor? {
        get { color(forKey: "backgroundColor") }
        set { set(newValue, forKey: "backgroundColor") }
    }
}

UserDefaults.standard.backgroundColor = .red
UserDefaults.standard.backgroundColor  // r 1.0 g 0.0 b 0.0 a 1.0