1 teaspoon at a time, if needed, for desired consistency. Stir in desired amount of food coloring, and spoon into a piping bag fitted with a writing tip.
Place 1 cake layer on a cake stand or serving plate. Spread with half of ganache; sprinkle with 1/2 cup toffee bits. Top with second cake layer; spread with remaining ganache, and sprinkle with remaining 1/2 cup toffee bits. Top with remaining cake layer. Cover and chill 2 to 8 hours...