I can't stand these sort of diarama style tanks, honestly.
Imagine the maintenance involved, particularly if you've got any sort of substrate disturbing fish.
My niece wanted a themed tank as well, I can't remember what the cartoon was but I do remember that it's colour selection was what I would call unicorn barf... I had to convince her to just keep it to a themed poster on the back glass with colour coming from the fish instead.
More power to you if you have the patience and ability to keep it looking good for a long period of time, I'd personally always pick something that a bit of algae and bottom feeding fish wouldn't harm.