I see you have answered the question somewhat, but to provide a slightly more concise way without using regex to answer to the title question:
To change the colour of a length of text you need to know the start and end index of the coloured-to-be characters in the string e.g.
var main_string = "Hello World" var string_to_color = "World" var range = (main_string as NSString).rangeOfString(string_to_color)
Then you convert to attributed string and use 'add attribute' with NSForegroundColorAttributeName:
var attributedString = NSMutableAttributedString(string:main_string) attributedString.addAttribute(NSForegroundColorAttributeName, value: UIColor.redColor() , range: range)
A list of further standard attributes you can set can be found in Apple's documentation