[Lizard]

If you're running OmniFocus 1.0.3, the easiest way to fix it is to reset your preferences, by removing com.omnigroup.OmniFocus.plist from ~/Library/Preferences.

If you're running OmniFocus 1.5 Sneaky Peeks, you can reset all styles to their defaults with the 'Reset' button on the Style Preferences pane.