Thank you very much! I'm sorry heterochromia isn't an option. We did think about it but have yet to find a doable way for it to work for the system we have. If we do come up with a good enough method, it could be added as part of a post-release update. Though I can't say for sure if it will ever be very possible.
But we're definitely going to do our best to make that release date ^^. Happy future birthday to you!