Colors.swift

enum Colors: Int64  
{
    case black = 0x000000ff
    case white = 0xffffffff

    func color() -> UIColor
    {
        let red   = CGFloat((self.rawValue >> 24) & 0xff) / 255.0
        let green = CGFloat((self.rawValue >> 16) & 0xff) / 255.0
        let blue  = CGFloat((self.rawValue >>  8) & 0xff) / 255.0
        let alpha = CGFloat((self.rawValue      ) & 0xff) / 255.0
        return UIColor(red: red, green: green, blue: blue, alpha: alpha)
    }
}

extension UIColor  
{
    func highlight(withLevel highlight: CGFloat) -> UIColor {
        // ...
    } 
}

let blue5 = Colors.white.color().highlight(withLevel: 0.95)  

Fonts.swift

public struct Fonts  
{
    enum SF: String
    {
        case bold    = "SanFranciscoRounded-Bold"
        case regular = "SanFranciscoRounded-Regular"

        func size(_ size: CGFloat) -> UIFont {
            return UIFont(name: self.rawValue, size: size)!
        }
    }
}

let sf = Fonts.SF.regular.size(16.0)  

Style.swift

protocol Style  
{
    var headline: (UILabel)->() { get }
    // ... any reusable element in your UI
}

struct OrangeStyle: Style  
{
    let headline: (UILabel)->() = { label in
        label.font = Fonts.SF.regular.size(16.0)
    }
}

protocol Styleable {}

extension Styleable {  
    func apply(_ style: (Self)->())->Self {
        style(self)
        return self
    }
}

extension UILabel: Styleable {}

let style: Style = OrangeStyle()  
let title = UILabel().apply(style.headline)