This is a theme for the Cyanogenmod Theme Engine.
You MUST be using a ROM with the new theme engine and Theme Chooser to use it.
Along with the framework, many apps have been themed including Settings, Apollo, Browser, Messaging, Gallery, and other CM apps. The theme also features an awesome bootanimation, and wallpapers for your homescreen and lockscreen.
This paid version contains a few more themed apps which include Dialer, Contacts, Gmail, Play Store, Play Music, Google Now and Google Keyboard.
Download the theme and install it. You'll get a notification, Neon Red installed.
Go to Themes > Settings, select Neon Red and tick everything.
This theme was made to work with CM. It will work for other ROMs too but not 100% compatibility is confirmed.
If you face any issue or bug, you can mail me or you can post in my XDA thread - http://forum.xda-developers.com/showthread.php?t=2754747