ColoredSubviews.swift

import Foundation
import UIKit

extension UIView {
    var allSubviews: [UIView] {
        get {
            var viewsFound: [UIView] = [UIView]()
            return viewsFound
        }
    }
    
    convenience init(subviews: [UIView]) {
        self.init()
        subviews.forEach{ self.addSubview($0) }
    }
    convenience init(backgroundColor: UIColor) {
        self.init()
        self.backgroundColor = backgroundColor
    }
    
    func coloredSubviews(color: UIColor) -> [UIView] {
        var viewsFound: [UIView] = [UIView]()
        return viewsFound
    }
}

let view = UIView(subviews: [UIView(backgroundColor: .yellow),
                             UIView(backgroundColor: .red),
                             UIView(backgroundColor: .yellow),
                             UIView(subviews: [
                                UIView(backgroundColor: .red),
                                UIView(backgroundColor: .red),
                                UIView(backgroundColor: .white),
                                UIView(subviews: [
                                    UIView(backgroundColor: .red),
                                    UIView(backgroundColor: .yellow),
                                    UIView(backgroundColor: .white),
                                    UIView(subviews: [
                                        UIView(backgroundColor: .white),
                                        UIView(backgroundColor: .red),
                                        UIView(backgroundColor: .red),
                                        UIView(subviews: [
                                            UIView(backgroundColor: .white),
                                            UIView(backgroundColor: .red),
                                            UIView(backgroundColor: .red)
                                            ])
                                        ])
                                    ]),
                                UIView(subviews: [
                                    UIView(backgroundColor: .red),
                                    UIView(backgroundColor: .red),
                                    UIView(backgroundColor: .yellow)
                                    ]),
                                UIView(backgroundColor: .yellow),
                                UIView(backgroundColor: .red),
                                ])])

let redViews = view.coloredSubviews(color: .red)
let yellowViews = view.coloredSubviews(color: .yellow)
let allSubviews = view.allSubviews

print(redViews.count) // should be 11
print(yellowViews.count) // should be 5
print(allSubviews.count) // should be 25