Board Thread:Questions and Answers/@comment-27074482-20151013191323/@comment-26845384-20151016023935

The simplest way is usually the best way to get something in particular. With the Rainbow Dragon, that would be yellow and blue (typically an Air Dragon and a Water Dragon). If one or both parents are below level 15, you take away the chance of getting a Prime Energy Dragon to leave you with 10 possible outcomes.

Rainbow takes 14 hours to breed/incubate, but so do Mist and Patchwork Dragons, and you wont know which it is until you send it to the nest.