Problema: NSAttributedString toma un NSRange mientras uso una cadena Swift que usa Range

let text = "Long paragraph saying something goes here!"
let textRange = text.startIndex..<text.endIndex
let attributedString = NSMutableAttributedString(string: text)

text.enumerateSubstringsInRange(textRange, options: NSStringEnumerationOptions.ByWords, { (substring, substringRange, enclosingRange, stop) -> () in

    if (substring == "saying") {
        attributedString.addAttribute(NSForegroundColorAttributeName, value: NSColor.redColor(), range: substringRange)
    }
})

Produce el siguiente error:

error: 'Rango' no es convertible a 'NSRange' atribuidoString.addAttribute (NSForegroundColorAttributeName, valor: NSColor.redColor (), rango: substringRange)