Preheat the oven to 350ºF (175ºC). Prepare 8-inch round cake pans by greasing them and lining with parchment paper.

In a large mixing bowl, combine white cake mix, instant vanilla pudding mix, egg whites, milk, sour cream, vegetable oil, and both extracts. Beat for about 2 minutes on medium speed, then divide the batter in half. Color one half with green food coloring and the other with purple.

Pour green batter into one prepared cake pan and purple batter into another. Bake for 28-30 minutes, or until a toothpick comes out clean. Let cool in pans for 10 minutes before transferring to a wire rack.

In a separate bowl, whip the chilled heavy cream until stiff peaks form. Blend softened cream cheese and powdered sugar in another bowl until smooth, then fold in the whipped cream.

Cut cooled cakes into small cubes. Layer the bottom of serving jars with green cake cubes, followed by chopped Oreos and half of the cheesecake filling. Repeat with purple cake cubes and crushed Oreos.

Pipe the remaining cheesecake filling on top and garnish with half an Oreo and Halloween-themed decorations.

Chill the assembled trifles in the refrigerator for at least 1 hour before serving.