In advance: Mix 1/4 teaspoon of Gum-Tex into 2 oz. fondant. Roll out fondant into 4 in. circles, 1/8 in. thick. Using candy mold, dust inside largest dome with cornstarch and place fondant in mold; cut the excess. Cut eight arches in the dome borders with a knife; let dry in mold.
Bake cupcakes in blue baking cups. Cool completely. Prepare icing and ice cupcake tops smooth with icing.
Roll out ball of fondant 1/8 in. dia. Melt Candy Melts candy according to package directions. Unmold umbrella and attach ball to top with melted candy. Decorate umbrella with edible color markers. Attach umbrella to lollipop stick with melted candy. Let set.
Sprinkle cupcake top with brown sugar. Insert umbrella.