Preheat oven to 350°F. Spray a 9x13 cake pan with nonstick cooking spray.

Add the cake mix, water, vegetable oil, and egg whites to a medium-sized (2-3 quarts) mixing bowl. Use a handheld mixer on medium speed to combine cake mix ingredients until completely incorporated, and no visible cake mix lumps remain.

Equally divide the cake mix into 3 smaller bowls. (I recommend using glass bowls or even disposable bowls, since this is when you will be adding the gel food color. Glass bowls usually do not stain)

Add 3-4 drops of the blue gel food color, depending on how light or dark you are wanting, to one bowl. Stir well until no streaks of blue remain.

For the purple, add 5-7 drops, again depending on how light or dark you are wanting, to one of the remaining untinted cake batter bowls. Stir well until no streaks of purple remain.

Add 5-7 drops of the pink food color gel to the remaining bowl. Stir well until no streaks remain.

Drop spoonfuls of the tinted cake mix into the prepared baking dish. Once all of the tinted cake mix has been added, use a toothpick or bamboo skewer to gently swirl the tinted cake batter. Bake for 25-28 minutes, until a toothpick inserted comes out clean. (Keep in mind that all ovens bake differently, so begin checking the cake at the 22 minute mark) Remove the cake from the oven and allow the cake to cool completely.

Once completely cooled, using the handle of a wooden spoon poke holes in the cake, about an inch apart.

Add the cold milk and pudding mixes to a large (4-5 quarts) mixing bowl. Use a handheld mixer on low, or a whisk, to mix the pudding for about 2-3 minutes until it begins to thicken well.

Spoon the pudding into the holes until they are filled. Once the holes are filled, spoon the remaining pudding over the cake. Use either a silicone spatula or an offset spatula to spread the pudding.

Spoon the 8 ounce container of thawed whipped topping on top of the pudding layer. Use a silicone spatula, or an offset spatula to smooth the whipped topping over the pudding. Cover and chill in the refrigerator for 1 hour.

Remove the cake from the refrigerator. Sprinkle ½ cup of unicorn sparkle sprinkles over the whipped topping layer. Slice the cake 3 slices x 5 slices. Keep refrigerated until ready to serve. Store any leftovers covered in the refrigerator for up to 3 days.