Using a serrated knife, trim tops of cupcakes to make level. Add 1 drop gel-paste food coloring to 3 cups buttercream. Stir well to combine. Add more food coloring, a drop at a time, stirring constantly, until desired color is reached. Transfer remaining buttercream to a pastry bag fitted with a coupler. Frost tops of cupcakes with yellow buttercream in a smooth layer. Refrigerate for 30 minutes until set.
Make the shells: Fit the pastry bag with drop-flower tip. Holding bag at a 45-degree angle, with tip about 1/4 inch from center of cupcake, squeeze out frosting, lifting tip slightly, then pulling bag toward you. Stop squeezing to end in a pointed tip, stopping short of edge. Continue piping, touching each shell slightly to the next, and rotating cupcake as each is piped.
Make the pearls: Switch to a small plain tip, and pipe a series of pearls (or dots) in a U shape. Starting at tip of 1 shell, work out toward edge of cupcake and end at tip of next shell. Repeat until all shells are linked with pearls. Repeat with remaining cupcakes and buttercream. Refrigerate until set, about 30 minutes.