How do you use the appropriate color class for the current platform?

Solution 1:

Use conditional compilation and type aliases:

#if os(OSX)
    typealias Color = NSColor
    typealias Image = NSImage
#else
    typealias Color = UIColor
    typealias Image = UIImage
#endif

Then use Color instead of UIColor or NSColor:

self.gameView!.backgroundColor = Color(red: 0, green: 0.2, blue: 0.5, alpha: 1)

Edit 2016-01-17: As DDPWNAGE noted above, Apple has created SKColor with basically the same definition.