在实际开发中，由UI提供的颜色值往往是十六进制字符串如“#FFFFFF”,开发者往往还需要自己去计算转换，故用Extension封装，如：

extension UIColor {

    class func hexStringToColor(hex:String) ->UIColor{

        var cString: String = hex.trimmingCharacters(in: NSCharacterSet.whitespacesAndNewlines).uppercased()

        if(cString.hasPrefix("#")) {

            cString = (cString as NSString).substring(from:1)

        }

        if cString.count != 6  {

            return UIColor.white

        }

        letrString = (cString as NSString).substring(to:2)

        letgString = ((cString as NSString).substring(from:2) asNSString).substring(to:2)

        letbString = ((cString as NSString).substring(from:4) as NSString).substring(to:2)

        var r:CUnsignedInt = 0, g:CUnsignedInt = 0, b:CUnsignedInt = 0

        _ = Scanner(string: rString).scanHexInt32(&r)

        _ = Scanner(string: gString).scanHexInt32(&g)

        _ = Scanner(string: bString).scanHexInt32(&b)

        return UIColor(red:CGFloat(r) /255.0, green:CGFloat(g) /255.0, blue:CGFloat(b) /255.0, alpha:CGFloat(1))

    }

}