I did the decorated this cake with buttercream icing..... layering the colors ( swirl the blue for the sky, then the darker blue for the waves, then the tan for the sand). Sprinkle crushed graham crackers over the sand ( you could also use brown sugar). The seashells were made out of marshmellow fondant ( MMF). I molded them in a candy mold and brushed the color on using food coloring.... now I'm just marbling the color in when I make my fondant.