Prepare white cake mix, then divide the batter evenly among six small bowls. Following the chart below, dye each bowl a color. Purple 9 red and 6 blue drops Blue 12 drops Green 12 drops Yellow 12 drops Orange 12 yellow and 4 red drops Red 18 drops Evenly distribute the purple batter among the cups, then the blue, and so on. As you go, gently spread each layer of batter with the back of a spoon to cover the color underneath.
When you get your berries home, prepare a mixture of one part vinegar (white or apple cider) and ten parts water. Dump the berries into the mixture and swirl around. Drain, rinse if you want (though the mixture is so diluted you can't taste the vinegar,) and pop in the fridge. The vinegar kills any mold spores and other bacteria on the surface. Raspberries will last a week or more, and strawberries go almost two weeks without getting moldy and soft.
Chocolate Chip Whoopie Pies with Strawberry and Cream Filling...looks yummy