We can change the style of the placeholder by setting attributedPlaceholder (a NSAttributedString).

var placeholderAttributes = [String: AnyObject]()
placeholderAttributes[NSForegroundColorAttributeName] = color
placeholderAttributes[NSFontAttributeName] = font

if let placeholder = textField.placeholder {
    let newAttributedPlaceholder = NSAttributedString(string: placeholder, attributes: placeholderAttributes)
    textField.attributedPlaceholder = newAttributedPlaceholder
}

In this example we change only the color and font. You could change other properties such as underline or strikethrough style. Refer to NSAttributedString for the properties that can be changed.