Rubymine-sunlight-theme is a project mainly written in ..., it's free.
a theme inspired from XCode 4's Sunshine color scheme (yellow, warm browns, reds, and grey blues)
This color scheme is inspired from Xcode 4.
1) Copy the 'Sunlight.xml' file to your ~/Library/Preferences/RubyMine31/colors folder.
2) In RubyMine 3.1 (or higher) under Preferences > Editor > Colors & Fonts choose the Sunlight theme for your Scheme name.
That's it!