With references to @i-- Answer
Updated Swift 5
UISegmentedControl.appearance().setTitleTextAttributes([NSAttributedString.Key.foregroundColor: UIColor.red], for: .selected)
Updated Swift 4.1
UISegmentedControl.appearance().setTitleTextAttributes([NSAttributedStringKey.foregroundColor: UIColor.red], for: .selected)
Swift 3.1
UISegmentedControl.appearance().setTitleTextAttributes([NSForegroundColorAttributeName: UIColor.red as Any], for: .selected)
For Earlier Swift Version:
UISegmentedControl.appearance().setTitleTextAttributes([NSForegroundColorAttributeName: UIColor.red], for: .selected)