Hetero eyes are only available in Dawn of Eternity, our new game which has not been released yet. You will be able to access them via the character customisation!
If you want hetero eyes in Last Moon then you'll have to create a preset (a personalised skin just for you or another person) which will be added ingame for other people to see. If you've spotted people running around with glowing markings or moving markings etc then those are presets!