Using a standing mixer, combine all ingredients except the food coloring and beat until smooth and stiff peaks form
Scoop 1 1/2 C of frosting into the 3 bowls each
Mix in 1 color into each bowl
Scoop each color into its own piping bag
Scoop 2 C of frosting into the green frosting bowl and add more green food coloring into the frosting. Mix until combined
Cut the tips off the three disposable piping bags
Using the green frosting, pipe a thick ring round the outer edge of the top of the first layer of cake
Pipe a thick ring of purple frosting on the inside of the green ring
Pipe a thick ring of orange frosting on the inside of the purple ring
Repeat steps until you cant pipe any more rings
Remove the dome from the second cake layer
Place the second layer on top of the first layer of frosting
Repeat steps with the frostings
Repeat steps of removing the dome from the third cake layer
Place the third layer of cake onto the second layer of frosting
Using 1 3/4 C of the green frosting, frost entire cake