In Joomla 2.5 and Joomla 3 it is really easy to make a spesific menu item have different color or give it different css .
If you open the menu item you will see at the right that there is an option for difference css for this menu item
So , you can give this menu item a css class for example menucolor2
Then go to your mail css file and add this
where you can put your favorite color !