I have only seen it in dogs, horses and human. Matter of fact my husband has heterochromia, he has a blue and a green eye and my neighbors kid up in KY had two light brown eyes but the right eye had a darkbrown spot.
Wow, that's awesome! I've also seen it in cats, but most often I see it in dogs. I think it's such a cool trait and I can't believe it showed up in Ellie!