That sounds really cool! My virtual pets are based more on personality and how both user and pet interact with the site and others, etc. Ego is the currency and the world that the Amlgammas exist in is called ErgoFlux. I plan doing a system where you dont 'adopt' a pet, you 'claim a part of yourself' instead. Then to try and get that pet to 'join you' you'll have to be careful in how you answer or offer stuff to the pet! It could join you, refuse and leave, or take items when it leaves you gave it, or you'll have to give Ego, or itll run away etc but in other cases join.
As for base colors theres 6, each for the Ego Traits of the Amalgamma (for now). Dependent on how you treat it, its 'color' will change to reflect its Stats an Traits.
Mine has alot of fun mechanics, some not explained until you reach certain quests, others obvious but not fully revealed how they work.