There is two rainbow eggs a red and a blue.
Red: The red is on top of the blizzard castle. You can get it by playing the 8 chicken rescue, go to the very top of the cliff where the chicken is and either use a jet pack or ride Datch to the snow flake castle.
Blue:The blue in on a plate form in pirate island. You get the blue by playing Bamham's 8 chicken rescue, you go to the cannon with a jet pack egg behind it,(Don't go into the cannon)look around and you will see some green and blue rings over the water, use the jet pack to hover over there and get the egg.(Careful of sharks if you chose to walk on the egg or ride Kaboot.)