Hair color: Which brand do you recommend for bringing out natural highlight?

I have brown hair with minimal gold and red undertones. Yet, its looking really flat and I was hoping to buy some hair color to spice it up. what would people recommend-im not looking to do a whole new color but something that will make it look a bit more rich (and bring out the red just a bit more). Im looking for a warmer red too not a cold purpley red. Iwant a natural color