Maximus, my silver Unicorn, has sired a second (actually third) unicorn foal! This one is white as the driven snow! As with Cesar, this one is born in-game and unaltered!
Knight (extract the .sim file to your The Sims 3\SavedSims folder)
Note: The second unicorn foal was released into the wild - less than perfect - no horn, ugly coat, and the back half was almost twice as wide as the front half! :P