Color Vision Cake

This recipe appeared in a story for 50th anniversary of boxed cake mixes. The Color Vision Cake, developed by the Betty Crocker kitchens, uses the fruit gelatin powder of your choice to create a vibrant color and flavor. Recipe from General Mills.

1 (18.25 ounce) package pudding-included white cake mix
3 tablespoons dry gelatin powder from small box fruit-flavored
    gelatin; reserve remaining powder.

Frosting
Reserved gelatin powder
1/3 cup butter or margarine, melted
3 tablespoons evaporated milk, or more as needed
3 1/2 cups confectioners