asking why did you go onto my wall when im not even a chat mod or even an admin..?
but if you wish to know how to get a rainbow dragon one of the most popular combos is the Crystal Dragon and Blue Fire Dragon or the Seaweed Dragon and Firefly Dragon now these are not the only ways to get them but the more the different elements, the greater the chance. to increase your chances level them up higher and get a Breeding island, if you need gems go to the Friends page.
Just to clarify, it is not correct that the more different elements, the greater the chance. All combos have the same chance-there may be fewer fail options, or there may be a lower average fail time, but the chances don't change.