If you want the new Xcode 8 beta theme for use in Xcode 7, navigate to
~/Library/Developer/Xcode/UserData/FontAndColorThemes/ and copy/rename
I really like this new color theme and am going to use it as a replacement for my long time favorite Solarized Dark theme. I’m even going to try the new SF Mono font instead of Source Code Pro.
Now all I need is for Apple to release a dark mode for Xcode. I don’t like having so much white UI in an otherwise dark editor. The best I can do for now is invert the colors in macOS (and use a light color theme).