Here is my xcode 4 color theme. I mostly use it during my nightly cocoa programming sessions. I love dark backgrounds because I find them particularly soothing to the eye. This theme is based on the website color palette.
To install the theme unzip the file into your /Users/yourname/Library/Developer/Xcode/UserData/FontAndColorThemes folder.
Works especially well if combined with some good Jazz through your headphones… something like Miles Davis’s “Kind of Blue” for example :-) . Enjoy.