Og course, this brings up the question of why. If a natural animal is brightly colored, it is either warning predators that it is toxic/venomous/poisonous/stink-throwing/whatever or trying to attract a mate. Beak dogs are the top dogs (pun intended) of the predator world, as my first post shows [EDIT: 5-on-five against alligators has five dead beak dogs

and five alligators with yellow and brown wounds, one unconscious-all the more reason to stay hidden until someone makes them venomous.]; therefore it seems to be to attract a mate. However, that would imply that only the males (or maybe only the females) are garishly colored; for females (or maybe males) there is no reason to be garish, and in fact it is a disadvantage-how many swamps do you know that are rainbow-colored?
Yes, I know, get my science out of your fantasy.
(Or this:
They're so badass, they WANT everyone to know they're comin'.
Makes no biological sense, but this is DF.)