iOS 9.3 is coming in the Spring and will introduce Night Shift as well as a number of other new features.
Mac OS X Theme Change in Leopard Seed 9A410
Edit: Images removed per Apple Legal.
Images originally posted on Hackint0sh.org. Images are mirrored here. Alternative screenshots are posted on Flickr.
Apple also announced today that Leopard would be delayed until October, so these changes may not represent the final user interface.