ios 文字变色

extension UILabel{

func paint(aText:String,aColor:UIColor?,startIndex:Int,endIndex:Int){
self.text = aText
if (attributedText != nil && aColor != nil){
let attr = NSMutableAttributedString(attributedString: self.attributedText!)
attr.addAttribute(NSForegroundColorAttributeName, value: aColor!, range: NSMakeRange(startIndex, startIndex + endIndex))
attributedText = attr
}
}

func paint(aFirstText:String,aSecondText:String,sSecondTextColor:UIColor){
self.text = aFirstText + aSecondText
if (attributedText != nil ){
let attr = NSMutableAttributedString(attributedString: self.attributedText!)
attr.addAttribute(NSForegroundColorAttributeName, value: sSecondTextColor, range: NSMakeRange(aFirstText.length(), aSecondText.length()))
attributedText = attr
}
}

}