Prepare an 11 x 13 pan with cooking spray.
Add 1 cup boiling water to package of blue Jell-O. Stir until dissolved.
Pour 2/3 cup gelatin into pan and place in refrigerator to set (about 20 minutes).
Add Cool Whip to remaining mixture to bring level up to 2/3 cup. Stir until Cool Whip melts and color is blended.
Gently pour on top of set gelatin and place in refrigerator to set (15-20 minutes).
Repeat this process with green, yellow, orange and red gelatins.
Allow to set for 2 hours before cutting and serving.