Final_Heaven
Pro Adventurer
From what I gathered, Tifaret did have Tifa's appearance, and was a mix between Tifa and Aerith (since she was a Cetra and al). When they decided to kill her, they created Aerith's design, leaving Tifa's for a new heroine with a new role, and IF the Tifaret thing is true (which I think it does hold a lot of "omg that makes so much sense!") then split her features between the two heroines.
But it's really interesting that, instead of coming up with a new design for Tifa, which would make sense, instead they decided that this design would be for Cloud's true love interest. I don't know if they had gotten attached to that design specifically, probably since it does strike me as odd to do that. I expected proto Aerith to look more like herself (since I believed she was there first, but it was only in "role" that she was).
I don't really know if we even really need information on this.
It would be too coincidental for it to be a coincidence tbh.
So there's an Ultimania on this but proto-Aerith was named Tifa with Tifa's design and had 2 Cetra siblings. One of them was Sephiroth who had a design that looked like Vincent. And Cloud's proto-design looked a lot like Zack as well so maybe that was just a common thing to reuse old designs of current characters.
That's perhaps why Tifa and Vincent look like siblings with the straight black hair, light skin and red eyes.
Anyways, when they decided to create another heroine after they decided Aerith had to die, they took proto-Aerith's old name as well as old design and gave it to Tifa.
I do believe it's mentioned that they migrated some characteristics of proto-Aerith to Tifa as well.
I don't know when they discarded the Tifa design for proto-Aerith though. It might have been when they decided to create 2 heroines.
Would make sense to me just because Tifa and Cloud have contrasting hair and eyes colors that Cloud and Aerith don't.
Square has also talked about making Aerith's eyes green to contrast with Tifa's red eyes as well as making the long dress to contrast with Tifa's miniskirt which suggests to me that the Aerith design was made specifically as a parallel to the current Tifa after they had decided that there were now 2 heroines.