Note: the default terminal emulator on OS X is Terminal.app, not iTerm!
I recommend all Mac users to use iTerm rather than the default terminal - firstly because iTerm has some very nice features (like split panes and autocompletion), and secondly because it doesn't mangle your colours like Terminal.app does. You can download iTerm here: http://www.iterm2.com/.
- Download Selenized palette files from this folder.
- Open iTerm, go to Preferences, click on the "Profiles" icon and select the "Colors" tab.
- Click on "Load Presets", select "Import..." and choose one of the palette
files.
You have now added a new preset to iTerm, but it's not applied to any profile yet. - To use the preset, select a profile from the list on the left, click on "Load Presets" and choose a preset.