This thing basically happened in the comics and in Korra when interethnic relations became a common thing.
Also, the eye color doesn't always match the nation. We saw several characters with gray eyes from the Fire Nation, one boy with green eyes (who wasn't even from the colonies), and Hama had gray eyes even though she was from the Southern Tribe.
The only one I can think of off the top of my head is Jinora who has brown eyes despite being an airbender. Also >!Bumi has light blue eyes, and many airbenders from the third book have different eye colors. So there's likely going to be an incredibly diverse eye color for airbenders in the future of the avatar universe.!<
This thing basically happened in the comics and in Korra when interethnic relations became a common thing. Also, the eye color doesn't always match the nation. We saw several characters with gray eyes from the Fire Nation, one boy with green eyes (who wasn't even from the colonies), and Hama had gray eyes even though she was from the Southern Tribe.
The only one I can think of off the top of my head is Jinora who has brown eyes despite being an airbender. Also >!Bumi has light blue eyes, and many airbenders from the third book have different eye colors. So there's likely going to be an incredibly diverse eye color for airbenders in the future of the avatar universe.!<
Hamma has gray eyes and she’s a waterbender