SKColor extension: create SKColor from hex value

gistfile1.swift

import Foundation
import SpriteKit
import UIKit

extension SKColor {
    convenience init(rgba: String) {
        var red:   CGFloat = 0.0
        var green: CGFloat = 0.0
        var blue:  CGFloat = 0.0
        var alpha: CGFloat = 1.0
        
        if rgba.hasPrefix("#") {
            let index   = advance(rgba.startIndex, 1)
            let hex     = rgba.substringFromIndex(index)
            let scanner = NSScanner(string: hex)
            var hexValue: CUnsignedLongLong = 0
            if scanner.scanHexLongLong(&hexValue) {
                if countElements(hex) == 6 {
                    red   = CGFloat((hexValue & 0xFF0000) >> 16) / 255.0
                    green = CGFloat((hexValue & 0x00FF00) >> 8)  / 255.0
                    blue  = CGFloat(hexValue & 0x0000FF) / 255.0
                } else if countElements(hex) == 8 {
                    red   = CGFloat((hexValue & 0xFF000000) >> 24) / 255.0
                    green = CGFloat((hexValue & 0x00FF0000) >> 16) / 255.0
                    blue  = CGFloat((hexValue & 0x0000FF00) >> 8)  / 255.0
                    alpha = CGFloat(hexValue & 0x000000FF)         / 255.0
                } else {
                    print("invalid rgb string, length should be 7 or 9")
                }
            } else {
                println("scan hex error")
            }
        } else {
            print("invalid rgb string, missing '#' as prefix")
        }
        self.init(red:red, green:green, blue:blue, alpha:alpha)
    }
}

// How to use
var color = SKColor(rgba: "#545454")