Rainbow Birthday Cake

1 package cake mix (any flavor)
Water, oil and eggs called for on cake mix package
Assorted food colors
1 tub fluffy white ready-to-spread frosting
Assorted colored sugar

Heat oven to 350 degrees. Grease bottom only of rectangular pan, 13x9x2 inches. Make cake mix as directed on package, using water, oil and eggs. Pour into pan. Randomly place 6 drops of food colors over batter. Cut through batter with knife several times for marbled design.

Bake as directed on package or until toothpick inserted in center comes out clean. Cool completely, about 1 hour.

Spread frosting over cake. Sprinkle colored sugars on frosting