This is straight from the Jell-o site. This is also good made into a 9x13 layer cake with one flavor Jell-0 (orange is our favorite) and topped with the Quick and Fluffy Frosting.

Holiday Poke Cake

2 baked 9-inch round white cake layers, cooled
2 cups boiling water
1 pkg. (4-serving size) JELL-O Brand Gelatin, any red flavor
1 pkg. (4-serving size) JELL-O Brand Lime Flavor Gelatin
1 tub (8 oz.) COOL WHIP Whipped Topping, thawed

PLACE cake layers, top sides up, in 2 clean 9-inch round cake pans. Pierce layers with large fork at 1/2-inch intervals.

STIR 1 cup of the boiling water into each flavor of dry gelatin mix in separate bowls at least 2 minutes until completely dissolved. Carefully pour red gelatin over 1 cake layer and lime gelatin over second cake layer. Refrigerate 3 hours.

DIP 1 cake pan in warm water 10 seconds; unmold onto serving plate. Spread with about 1 cup of the whipped topping. Unmold second cake layer; carefully place on first cake layer. Frost top and side of cake with remaining whipped topping.

REFRIGERATE at least 1 hour or until ready to serve. Decorate with fresh raspberries, if desired. Store leftover cake in refrigerator.

Quick Fluffy Frosting

1 1/2 cups cold milk
1 envelope DREAM WHIP Whipped Topping Mix
1 pkg. (4-serving size) JELL-O Instant Pudding & Pie Filling, any flavor

BEAT milk, whipped topping mix and pudding mixes in deep narrow-bottom bowl with electric mixer on low speed until blended.
BEAT on high 4 to 6 minutes or until mixture forms soft peaks. Makes about 3 cups or enough to frost 2 (8-or 9-inch) layers or 13x9-inch cake. Store frosted cake in refrigerator. For high altitude areas, reduce beating time to 2 to 4 minutes.