Here's a screenshot:
All you need to do is find your 'theme' folder (it may be nested a bit but it should be in the application folder somewhere under /lib/) and replace it with this folder. I created this on a mac and it's theming version 1.0 of the IDE, but I'm guessing the theme folder is the same for all platforms. Make a backup of yours before you drop this one in just in case though.
You'll need to restart the Arduino IDE for the changes to take effect, but then you can sit back and let your eyes thank you!
Hope you like it.