Use attributed string:
// Define attributes
let labelFont = UIFont(name: "HelveticaNeue-Bold", size: 18)
let attributes :Dictionary = [NSFontAttributeName : labelFont]
// Create attributed string
var attrString = NSAttributedString(string: "Foo", attributes:attributes)
label.attributedText = attrString
You need to define attributes.
Using attributed string you can mix colors, sizes, fonts etc within one text