Swift extension for creating a UIColor from a hex string or number

UIColor+Hex.swift

extension UIColor {
    convenience init?(hexString userHexString: String, alpha: CGFloat) {
        var hexString:String = userHexString.stringByTrimmingCharactersInSet(NSCharacterSet.whitespaceAndNewlineCharacterSet())
    
        if (hexString.hasPrefix("#")) {
            hexString = hexString.substringFromIndex(hexString.startIndex.advancedBy(1))
        }
    
        let hexNum = CGFloat(strtoul(hexString, nil, 16))
        self.init(hex: hexNum, alpha: alpha)
    }
    
    convenience init?(hex: CGFloat, alpha: CGFloat) {
        let mask = 0xff
        let hex = Int(hex)
        let red   = CGFloat((hex >> 16) & mask) / 255
        let green = CGFloat((hex >> 08) & mask) / 255
        let blue  = CGFloat((hex >> 00) & mask) / 255
        self.init(red: red, green: green , blue: blue, alpha: alpha)
    }
}