• Using a greased 9x13 baking dish, prepare, and bake  the white cake mix according to the back of the box
• Let it cool for at least an hour
• Poke several holes in the cake using a straw, wooden skewer or fork
  
• For a different look...You could vary the depth of each hole
• To achieve a rainbow in each slice...I spaced mine very close together - about 1/2 inch apart

Prepare each color of jello separately:

• Open a jello package and pour half of the package into a squeeze bottle
  
• Add about 1 cup of hot water to dissolve the jello. Close the cap on the bottle, and carefully - over the sink - swirl the liquid around until I the jello is dissolved
• If using several colors, as I did - Squeeze the jello into only some of the holes you have poked in the cake
• Follow with the other jello colors, using the same procedure - filling up every hole that you have poked into the cake
• *If using only one color - finish up by pouring the other half of your jello powder into your squeeze bottle once it is empty and fill it up again. Finish squeezing the dissolved color into the poked holes 
• You will most likely have some jello from each color left over 
• Cover the cake and place it in the refrigerator so jello can set up

Whipped Topping:

• Using  a mixer - Whip the whipping cream and powdered sugar until soft peaks form
  
• Pour the instant vanilla into a separate bowl, and add the cold milk
• Mix together, and let set up
• Fold the vanilla pudding into the whipped cream
• Spread on cake
  
• Add sprinkles
• Cover and refrigerate until serving