Preheat oven to 325°. Grease and flour a bundt pan.
Prepare cake mix according to package directions.
Spread 1 1/3 c. batter evenly into bundt pan. Place another 2 Tbsp of batter in a small bowl and reserve for later.
Take six more bowls and divide as follows. Put 2 Tbsp into a bowl and tint with purple food coloring, 1/4 c. into another bowl and tint with blue food coloring, 1/3 c. of batter tinted green,
1/2 c. batter tinted yellow, 2/3 c batter tinted orange, and the remaining batter red.
Spread the red batter in a wide ring onto white batter to within 1/2 in. of pan edges. Spread a ring of orange in the middle of the red ring, leaving some red visible on each side. Repeat by spreading remaining colors in the middle of the previous layer, in rainbow color order. (Each ring will be narrower than the previous layer.) Top with reserved white batter spreading over purple ring only.
Bake 40-45 minutes or until a toothpick inserted in center comes out clean. Cool completely in pan and then flip onto serving plate.
In a medium sized bowl beat the whipping cream until it starts to thicken. Add powdered sugar and vanilla. Beat mixture until it forms stiff peaks.
Serve cake with whipped cream clouds.