That seems like it could be broken easily in an eternal format

Yeah, a mana of any color for each lost pint of life is insane. I just changed it to be more like Phyrexian Arena or something.

Well, now it's useless. Upkeep mana doesn't help you with anything. Should be "at the beginning of your precombat main phase." That would be an interesting ability.

That's just stupid template problems. But I like the basic idea; undead mana-elves. Though given this costs 3 in two colours - maybe it should be a little bit stronger? Or a bit cheaper?

Thanks for bearing with me. I made the mana cost easier to pay, and made it an Elf so it could have those sweet tribal benefits.

Reminds me of Vesper Ghoul and Blood Celebrant. However, I think both of those are color bends, especially the Ghoul since it adds (not just fixes) mana of any color. I would also count Deathrite Shaman as a color bend although the concept of giving a slice into mana dorks and/or rituals by tieing the effect with exiling (lands) from (your) graveyard is rather interesting and worth of note.

Also as far as Zombie Elves that add mana go, Llanowar Dead exists.

Does this need to be a hybrid card instead of a "true" multicolored?

No. It doesn't.