I have a themed pet that looks nothing like how it should look in the codex. I was wondering how my pet can have so many incorrect genes and still be labeled as a themed pet. I was also wondering how much colour variation there is for themed pets.

the only themes with a set of specific traits are Restricted Themes such as the Cute Witch Zolnixi or the Storm Serpent Aeridini.
themed pets can come with any traits available without the use of trait disruptors or scrolls (how you can put Restricted Traits on pets that don't normally have them) when they are caught or grown.

as for color swing it depends on the colors of the themed pet, some darker or lighter colors will tend to be more off from the original theme than brighter or more vibrant colors.

Thank you! I was just comparing to the theme codex and was confused why mine don't look like them. So really the only defining factors for the pet being themed is that the pet is born from 2 of the same themed pet?

The thing that makes a pet themed is the purple tag and orange star on the bottom of its page, if it's blue that makes it a purebred theme. ^^

Thank you!