Use struct in Swift namespace

MyDefaultColors.swift

extension UIColor {
    
    struct MyDefaultsColor {
        
        private init(){}
        static let Red = UIColor(red: 1.0, green: 0.1491, blue: 0.0, alpha: 1.0)
        static let Green = UIColor(red: 0.0, green: 0.5628, blue: 0.3188, alpha: 1.0)
        static let Blue = UIColor(red: 0.0, green: 0.3285, blue: 0.5749, alpha: 1.0)
    }
    
}