You have a good color already. I would probably add some golden brown or reddish tone highlights. With the length of your hair, The highlights look great with styling your hair.

Since you have an olive complexion I would not go any lighter than brown. -- John

i think brunette would be your best bet. You can play with lighter brown but I wouldn't suggest anything lighter than a medium-dark brown. If you are looking to implement a new look, I would suggest to go in with panels or streaks. Even the Ombre technique or peek-a-boo highlight would look really good. As far as good color combinations to achieve these looks, I would suggest caramels, coppers, chestnuts, reds. Have fun!

Your hair color is really pretty. For something different, you could try a deep, chocolate brown or add some carmel highlights. Try using the "Makeover" tool and try on some different shades.

I think your hair color fits you just fine. Maybe you could darken your brows a little bit for perfection ;)