I would be nice to have one that as a "pup" is all gray, but as it matures it gains zebra stripes.
It might be cute to have one with brown paws, blue body, and yellow tips on it's ears and tail and then when it's middle aged it gains sprouts on it's legs. When it becomes an adult it could be flowery.
Since they apparently have horns when they grow up, one with a red nose and deer markings would be cool. Maybe have two types one with the red nose and one without, and the red nosed one is available only on Christmas eve and Christmas.
An adoptable with a red rose pattern on it's side and on it's belly and legs rose petals. It could have a black base.