maybe the reason is obvious to you...but if you are encouraging pet dyes ( which I am not) why not Dreads and Hiryus?
They already stated that creatures who already have chances to spawn as different colors wouldn't be dyable, so your woes about your cu can be put to rest as cu sidhes and hiryu's wouldn't be dyable.
Dreads are a jet black color, and hiryu's have a spawn chance for special colors.
Honestly, instead of adding pet dyes, I would rather them just add varients of pets in wide use now. Like frost based mobs, or poison based mobs, or energy based and give them different colors.
Would give tamers more variety in the types of pets they can use.
Although if they add pet dyes, I hope they make it so that tamers with veterinary can make them by harvesting blood/skin/scale samples from beasts and converting them into pigments or something.
Vet needs something to make it worth using.