Two colours in each eye. Rare?

At 3 months old, our kitten Bonnie had a blue ring around the pupil and yellow on the outside. She's now 8 months old and they're green in the middle with yellow outside. I believe it's called central heterochromia but I haven't seen any similar photos. Plenty with odd eyes and patches in the eye but none like this. So I'm wondering how rare it is? Has anyone got or had a cat with eyes like this? Will they eventually turn full yellow?

This is Maggie, the first kitten born in my cattery. As you can see her eyes were green on the inside and goldish yellow on the outer edge. They were that way for several years then one day, when she was about 4 years old I noticed her eyes were green. In certain lights they still appear what I call celery green on the outside edge.
Please excuse the way she is shaved down in this photo. She is a demon to try to groom, which is why she stayed here instead of going to a pet home. I was afraid that a pet owner would not put up with her attitude toward grooming as she will bite,scratch or do anything she can to avoid it. I told my husband that we are responsible for her so she was staying. He agreed.

Nice to see our Bonnie isn't alone!