Looking for a fantasy shoujo manga with a girl with WHITE hair that could use magic despite living in a world where only those with BLACK hair can.

She is actually someone that is reincarnated (but still from the same world) who died after her boyfriend "betrayed" her (don't remember so much how it happend). And, in fact, he too is reincarnated and in this life is a prince. They both kept their old memories of each other.

They found each other "again" when the MC is invited to the castle, together with other girls that can use magic, trying to pass some tests (don't remember what for).

Sounds like https://www.mangaupdates.com/series.html?id=152751

That's the one. Thank you. ☺☺