They call it the emerald coast of Florida, and with good reason! The water is indeed an emerald color, due to it's clarity and the color of the bright white sand. The emerald coast stretches from Panama City through Pensacola Beach, with Destin and Fort Walton Beach being among the most popular places in between. I recommend avoiding Pensacola Beach since it just gets too crowded and traffic across the bridge can be a nightmare.
While these beaches are among the best out there during the warmer months, this is north Florida, and it gets downright cold here in the winter.