In DragonVale for the iPhone and iPad, the Seasonal Dragon is the only dragon so far said to change its appearance over time, changing colors as the seasons change.
To breed the Seasonal Dragon, you must mix dragons with a total of air, fire, and plant attributes. Blazing + Plant or Blazing + Tree, etc. If you get a 48 hour incubation time then you’ve got it.
Check out my DragonVale Breeding Guide for more dragon breeding combinations.