Hex string <=> UIColor conversion in Swift

YLColor.swift

import Foundation
import UIKit

extension UIColor {
    convenience init(hexString:String) {
        let hexString:NSString = hexString.stringByTrimmingCharactersInSet(NSCharacterSet.whitespaceAndNewlineCharacterSet())
        let scanner            = NSScanner(string: hexString)
        
        if (hexString.hasPrefix("#")) {
            scanner.scanLocation = 1
        }
        
        var color:UInt32 = 0
        scanner.scanHexInt(&color)

        let mask = 0x000000FF
        let r = Int(color >> 16) & mask
        let g = Int(color >> 8) & mask
        let b = Int(color) & mask

        let red   = CGFloat(r) / 255.0
        let green = CGFloat(g) / 255.0
        let blue  = CGFloat(b) / 255.0

        self.init(red:red, green:green, blue:blue, alpha:1)
    }
    
    func toHexString() -> String {
        var r:CGFloat = 0
        var g:CGFloat = 0
        var b:CGFloat = 0
        var a:CGFloat = 0
        
        getRed(&r, green: &g, blue: &b, alpha: &a)
        
        let rgb:Int = (Int)(r*255)<<16 | (Int)(g*255)<<8 | (Int)(b*255)<<0
        
        return NSString(format:"#%06x", rgb)
    }
}

A simplified version of eMdOS with Alpha support and optionals. I use it to get the colors from a JSON without worrying if it's defined or not.

extension UIColor {
    convenience init?(hexRGBA: String?) {
        guard let rgba = hexRGBA, let val = Int(rgba.replacingOccurrences(of: "#", with: ""), radix: 16) else {
            return nil
        }
        self.init(red: CGFloat((val >> 24) & 0xff) / 255.0, green: CGFloat((val >> 16) & 0xff) / 255.0, blue: CGFloat((val >> 8) & 0xff) / 255.0, alpha: CGFloat(val & 0xff) / 255.0)
    }
    convenience init?(hexRGB: String?) {
        guard let rgb = hexRGB else {
            return nil
        }
        self.init(hexRGBA: rgb + "ff") // Add alpha = 1.0
    }
}

Usage:

let newColorWithAlpha = UIColor(hexRGBA: "#aabbccdd") ?? UIColor.white
let otherColor = UIColor(hexRGB: "#aabbcc") ?? UIColor.blue

@Invisible66 Updated it to Swift 4: https://gist.github.com/pvroosendaal/5aca45dff84590ab4d92d7b151b21839