Iris Dark is a flat theme that uses varying shades and tones to create distinction and a modern experience. It supports Gtk 3.10, Gtk 3.12 and Gtk 2 (using the Murrine engine).
The icons are not released and the shell theme is Elegance Colors: fav.me/d525x6c
If you wish to, you can buy the theme to help support it's development.
Happy tweaking License: GPL 3.0
EDIT: I want to say thanks to everyone who's favourited, downloaded or even viewed the theme! I never expected it to get so much attention from everyone! Thanks guys
Double EDIT: Daily Deviation!! Wow! Thanks again everyone!
2014.08.04: Fixed bugs with Java app menus and distortion of insensitive menu items in Gtk2.
2014.06.23: Hacky support for new aura-based Chrome.
2014.05.10: Updated to Gtk 3.12 and added support for new Unity theming.
2014.03.16: Fixed bugs in Chrome as well as other tweaks.
2014.02.17: Tweaks and experimental Unity CSD support for Ubuntu 14.04
2014.02.02: Fixed bugs with Firefox and tweaked Terminal.