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1
Preheat oven to 350 degrees F. Lightly spray 2 (8-inch) round cake pans with cooking spray; set aside.
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2
In a large mixing bowl, beat together cake mix, water, oil, egg whites, and vanilla on low speed using an electric mixer for 30 seconds.
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3
Scrape down sides of bowl using spatula and beat on medium speed for 2 minutes.
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4
Divide batter into the prepared pans evenly and bake in the oven for 32 to 36 minutes or until a toothpick inserted into the center of the cake comes out clean.
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5
Use oven mitts to remove pans from oven and let cool for 10 to 15 minutes before turning over onto wire racks to cool completely.
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6
Trim off the tops of the cakes, to make a smooth surface.
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7
Place 1 tablespoon of each flavor of gelatin in separate small bowls.
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8
Stir 1/3 cup boiling water into each and stir until dissolved.
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9
On the trimmed sides of the cakes, splash the different gelatin all over the cakes.
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10
Cover cakes, separately, with plastic wrap and refrigerate for 3 to 4 hours.
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11
Remove cakes from refrigerator.
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12
Unwrap the cakes and place 1 cake on a plate or stand and spread white icing evenly on top.
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13
Place the second cake on top and finish icing cake, top and sides with the white icing.
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14
Randomly place big dollops of the colored decorating icing all over the iced cake.
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15
Using a small spatula, swirl the dollops together to create a tie-dye/rainbow effect on the cake.
