Spoon frosting into large bowl. Stir in enough food color until desired yellow color. Using serrated knife, cut rounded top off 8-inch cake. Place 8-inch cake, cut side down, on serving plate; spread 1/2 cup frosting over top. Place 9-inch cake, rounded side up, on frosted cake. To "crumb-coat" cake, spread thin layer of frosting over side and top of layered cake to seal in crumbs. Freeze cake 30 to 60 minutes.