Never gave thought to different coloured eyes, my brother has one blue/grey the other green, perhaps growing up with this around one does not find it odd.
Why would anyone want to change their eye colour, you are born with what you have. Myself I have green eyes, only once ever did anyone react saying it out loud which took me off guard a bit, I suppose if you don't live with it is a little different.
You would not find it unusual to see two different coloured eye then Joan. I really only know the one person from school and she had the same coloured eyes as your brother. I’m happy he wasn’t singled out because of the eye heterochromia.
Actually he was popular with the girls LOL, shy so never took advantage!